Ive spent alot of time on the phone with MyLaps USA.

Our club just upgraded to the new RC4 Box, and the MRT's do work, but dont count every lap. Ill get 4-5 laps in, then a miss of a couple, then hit a couple..
Fortunately we have 20 rechargeable house transponders that do work (already tried them).

RC4 was designed to stop cloning, and they have accomplished it. From my understanding, the new box filters out the signal alot better than rc2 or rc3. So if it is filtering the signal better, that means the MRT is not a exact copy of the amb signal or MRT got it as close as they could to the original.

The new RC4 Transponders are due out soon (not the hybrid) and RC2 and RC3 versions 1,2,3, and some 4's will not pick up the new transponders. So clubs are forced to upgrade for 330 bucks right now, or wait it out and spend over 3000 dollars after they discontinue the deal.
I have 2 MRT's and will trade them in asap before that deal goes away (its 40 bucks for trade in on pt's and clones), and get new rc4 pt.