I have a 275 and love it. It compares very, very close to my Inovonics monitor modulation measurements but wouldn't really want to use it to try to squeeze out every single % of mod in a competitive situation. Of course the FIM function is relative but I was easily able to prove that an interfering translator to one of my Class A clients was running an omni antenna where they should have been on a Scala yagi.
Willie, I don't know of a cheaper receiver that will give a reasonably repeatable sig strength measurement (other than a few LED's) than the 275 other than maybe an SDR RX & software. Those can be had for less than $20.