I find that the legacy remote gets much stronger reception than my cab-1 system. I can move all over the house. I also feel that it provides obvious feedback to the user, that a command has been accepted (in the form of a beep on the keypad, etc.). With the cab-1's soft-style keys, I was never sure if my button press was actually taking.
The legacy speed dial has notched stops where the Cab-1 is free-spinning and thus, speed can easily be accidentally altered on the cab-1.
As far as operation goes, I haven't noticed much "improvement" when operating my TMCC locos but there is also no downside as far as I can see.