They are both really great radios. I have used the MX-V and it had all the important features you need and it will have a MUCH better response/feel over your rtr radio

There are only a couple things the MT4 has over the cheaper radio imo.. One, the MX-V feels 'cheap' to me. It just does, not much you can do to change it.. Also, the MT4 has telemetry so you get the temperature gauge which is very nice.

Ultimately, if you don't mind the cheaper feel (toyota) then there aren't really any important reasons to upgrade to the radio that costs twice as much (cadillac's are gross so I'll say BMW )