Is NGSpice known to get worse accuracy than others?

I have been losing sleep over a project that I’ve been intensely working on. For this project I need some kind of analog multiplier, analog divider, or voltage-controlled amplifier. I have tried to simulate a variety of such circuits, none of which got the expected results. Some of them have used transistors, some op-amps, and I’ve tried using the official VCA810 subcircuit spice model from Texas Instruments, but non of them have behaved as they should.

Normally, the results don’t even resemble anything close to what I’m looking for. Just now, I tried imitating exactly what’s in this YouTube video of LTSpice. I go something that somewhat resembles the expected result, but the waveform is grossly distorted.

What is going wrong? Is this just a problem that NGSpice always has?

There is no reason for the NGSpice engine to give worse results than any competitor.
What does vary are the device models. Many transistor models are far from reality at very low and high currentscurrents.

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