I have an earlier version of this:
ONN 43" 4K
I got it for less than $200 USD.
Ubuntu Mate 20.04.1 LTS set to 3840x2160 @30Hz and Mate Tweak HiDPI set to HiDPI. With HiDPI set to “Regular” most OS text is stupid small on the screen.
I would like a dual monitor setup, but I do not have the physical space for such. I can often get away with multiple windows on the one TV panel and changing the zoom level for each window (Ctrl+mouse-scroll).
30 Hz is getting a bit slow even for CAD
I do wish the refresh rate was higher, however I do not perceive any issues with the current refresh rate.
Very happy with the current results for the price.
Can you blink your eyes faster than 1/30 of a second ? 
No, but you can just start to see annoying jerkiness when at about that point.
Is the refresh limit the monitor, the graphics card or even the HDMI cable limited?
Drawing a 4K display eats bandwidth
Modern LCDs and OLEDs don’t produce visible flicker when refreshing, unlike CRTs and plasma screens. For a static image a refresh rate of only 1Hz is obviously fine (dynamic refresh rates down to 1Hz are used in a mobile phone I’ve just been reading about, but I can’t remember what model it is - the OnePlus 9, possibly?).
The problem comes with motion. When scrolling, or dragging CAD objects across the screen, the refresh rate reveals itself as jerky motion. It is so common we’ve all got used to it, but it is widely accepted that when using a scroll-heavy product such as a mobile phone, refresh rates of 120Hz make a very substantial difference over the widely accepted 60Hz.
So there isn’t really an ideal refresh rate because it depends on how much movement there is on the screen. Also, some people are much more sensitive to motion judder than others, so individual needs vary.
Having said that, I would have thought a refresh rate of 30Hz would be OK for CAD, for most people. After all, the classic frame rate for a movie is only 24fps, and even now loads of vids on YouTube are 30Hz. Personally I find a 60Hz LCD or OLED screen just fine for all computing work, unless it’s a CRT or plasma screen, in which case I can see flicker until the refresh rate is above 75Hz.
I did that same thing (43" 4K 30hz TV) for several years. The lag is 100% noticeable and annoying even for office work or web browsing. Do not recommend.
We need to be careful here. Lag is different from refresh rate. Lots of TVs do heavy processing on the incoming video to sharpen it up, brighten the colours, etc. Plus they typically try to use the cheapest possible chip set. This can introduce noticeable lag.
I’ve not noticed any lag issues on a computer monitor for normal desktop use (although I’m told gamers have to be picky). Mostly it’s about getting a flicker-free screen and judder-free scrollling and motion.
These days it’s probably also common to use big TV’s a s displays for game consoles. Which produce excellent video quality by themself, do not need “heavy processing” but do benefit from low latency.
It’s probably possible to disable or at least influence the amount of processing / lag of many TV’s, but you’ll have to read the manual and it’s probably written in some obscure language intended for nitwits. But then again, the cheapest TV’s may be stripped of any possibility to output a decent picture.
Yes, IIRC, 25 frames per second is about the lower limit for our eyes to turn a sequence of differing photographic images into motion pictures.
Thank you for clarifying, SteveT.
Yes, lag can be terrible even with a good refresh rate. But the refresh rate sets a lower limit.
Before you run out and buy that 4k TV, try turning down to 30Hz on your current monitor and see if bothers you.
Talking about terrible lag…
Here in europe there is some thing called soccer, which is apparently quite popular. Apparently lag was bad enough sometimes that people heard a lot of noise and cheering from houses around them, before they saw on their own television whether a goal was made or not. Apparently there were several seconds difference in lag, depending on the route of the TV signal to your home.
That obscure language is often referred to as “Chinglish” where I am. 
That may well be a censorship delay rather than a lag.
In Australia there is a 7 second delay on live television and radio to allow for removal of inappropriate comments.
Some European television providers may use this same technique.
Yeah, I do that sometimes, depending on which way my mind wanders.
On average though I’d think my contribution to this forum is positive.
10 minutes for the UK sourced news in Malaysia, in case the story is sensitive.
Anyway the point is that broadcast television is not “interactive” (except for the New Year countdown) while CAD is
Yeah, in my opinion dual monitors is definitely the way to go!
(And I don’t mean like the 1980’s CAD stations, where a large monitor displayed your work while you entered commands and did housekeeping on a second, small, monitor.)
At various stages of a design effort I may have:
A circuit simulator on one display, and KiCAD Schematic on the other;
Schematic editor on one side, and data sheet(s) on the other;
Schematic editor on one side and PCB layout on the other;
PCB layout on one side and footprint editor on the other;
Different versions of a schematic or layout, one on each side.
Rarely, I’ll stretch a schematic or layout across both monitors so I can get a more complete perspective of “the forest”, after concentrating on the details of “the trees”.
For the last year, I may have a videoconference on one side and related document(s) on the other
It’s the digital equivalent of the Good Ol’ Days (formerly known as “these difficult times”) when I covered half the acreage of a drafting table with data books, application notes, reference manuals, and product samples, leaving barely enough room for whatever I was working on.
I have a pair of 10.5"x18.5" (22" diagonal) monitors set side-by-side. I usually position my chair so I’m mainly in front of one, with the other more in my peripheral vision, an easy head-turn to the side. One guy at work likes dual monitors stacked vertically. There’s probably lots of room for perceptual psychologists to investigate the effects of spacing and physical arrangement.
Dale
I used to have 2 monitors back in the dark ages…life was terrible and replacing one monitor periodically at a time was a huge mistake I can now see in hindsight that always resulted in different drivers, sizes, res and problems. As a mechatronics engineer working on several mech, electronic, graphic EDA’s I made a leap of faith about 7 years ago now…to go to a single 34" wide Samsung curved L834790CN8 monitor and my graphic life is so much better now…my focus is now solely on the design issues not on how to view it also. If you do anything more graphics wise than playing games then I assure you of great advice. Even my laptop can plug into the HDMI2 of the monitor so that a portion (25% in my profile) is auto displayed as PIP on the monitor. Add the Microsoft PowerToys FancyZones (win10 although I believe this will be std in Win11) life is as good as it gets to have some apps just auto open up in a section I preallocated…such as dev systems and main browser goes to right half of monitor and then Outlook to left 1/2 etc.
So if you even vaguely think that your monitor is much of a sticking issue focus then I cannot highly enough recommend the items above…large good monitors might be a touch more expensive however I have done some amazing things for 7 years and cannot ever see an upgrade coming for a very looong time.
Driverwise and resolutionwise to keep up with latest trends & apps it’s had a perfect score. Reliability it’s been almos perfect…only two issues that every now and then the screen auto off stops working however that’s has been a Win10 issue so easy to fix. Second issue is that the screen after a few years stopped coming out of hibernation but googling pointed to a failing power supply. This was easy to fix as the power supply is external and getting one for $100 through the web was as easy fix.
Looking at engineers and graphic design desks often I always see a bunch of monitors and smile that the secret is not yet out even after so many years?
Regarding STM32CubeIDE, I wrote a small tool to improve its icon.
Hope it is useful.