Ok I bought one - RMR-C450, so far so good, it detects where it needs to, filters out lots of false alarms. Medium range detection. You don't need miles of warnings - they normally only 'do' the cars they can see, just needs the edge which is what this unit gives you. The voice is good, tones pleasant - bit on the quiet side but can be heard over the radio, auto mute is good, as are the two City filters. Mounted on the window it dosen't 'bounce' about like the Bel unit- probably because it's half the weight.
I've seen the videos from Radar Roy (he does seem very anti RMR - but wouldn't any ex-cop trying to protect his buddies interests. Although he does support the very expensive top of the range Bel units).
RMR do not claim to blind out radar / laser - that would give the police every excuse to stop you. Just a few seconds of confusion to let you adjust your speed down. This would not normally be obvious on a radar / laser unit.
It seems the American courts were very unhappy the units last year, when they prosecuted RMR for producing them - no smoke without fire as they say - it would not go to court if it didn't do what it was supposed to.
I just needed something to backup the sat-nav (which has all the fixed cams on it) - so far this little unit is doing the job, didn't break the bank and doesn't drive me mad with false alarms. The ticket rebate is useless in the UK anyway, and it only has to work once to pay for itself.