I have two of the 275's and just installed a MXT500 into my JKU, for the rigs where I do not use GMRS often, the 275 has worked great, love that you can stash it away somewhere and have the all in on microphone, only real complaint I have with it is when starting the rig with the radio on, the 275 seems to power off (Likely due to the soft momentary on/off that looses its latching during vehicle start). Not a deal breaker, but annoying when you forget to check its on after a stop and miss radio traffic. Both rigs I have it mounted in use NMO roof mounted 1/2 wave antennas and have very good SWR readings, and great range.
The MXT500 (conventional version with controls on radio) is yet to be tested in the field, but seems to work well, It was hard to get a decent SWR on the JK though, Due mainly to antenna location (mounted on the cowl with a Rugged Radio bracket) I tried four different antennas before finding one that I could tune to an acceptable SWR (two were around 2:1 and the little factory supplied one was at 3:1) I ended up with 1:4 SWR using a Laird BB4502NS no ground plane antenna which I can live with.
