The one thing a real tester will show is live engine data (On most OBD1 ECU's)
that can help troubleshoot issues.
Take the 02 into a Autozone and let them test it? If the O2 has more than 50 or 60 K on it the car might even run better. I just buy them from a local auto supply, since I'm OBD1 and the one that comes in the box is a Bosche sensor with the same markings as the one the dealer sells....
My 95 had a constatn O2 code that was caused by teh Meter to throttle body boot having a hole in it... a very very small hole.
Dave
Dave