My slider gauge works pretty well, and has for years.
As far as I know.
Probably.
At least it reads better than my air compressor.
Well, lower anyway, because the compressor shows 25 lbs higher pressure than the slider.
But only while/after filling; just connecting it shows a completely different pressure.
I'd use my bicycle pump on the car, which I believe to be more accurate, but I get enough exercise.
And the pump would only be more accurate at ~100-140 psi, which I'm sure would not end well...