I have never run an isolator, and I have always had consistent pressure readings with no leaks. I do use a needle valve to dampen the pulses from the pump, though. Both of my buddies with FP gauges used to run isolators, and they trashed them in favor of needle valves. One of them ruined a gauge even with the isolator.

Needle valve and direct plumb all the way here... No problems for over 5 years!