I have the 3PV which is inexpensive and extremely reliable IMHO. Simple to setup and use.
One thing the 3PV does not have is an adjustment for servo speed which has been discussed in detail on this forum. Alot of folks here swear by that feature but I'm old school so it's not an issue for me. Just a personal preference.
Not exactly sure if the 4PM has that function but I would imagine it does if that is important to you. I'm sure someone will chime in on that one.
I started using the servo speed on my gas mono this year and it helped a great deal in the corners. Before I used it my boat would spin out this way it will slowly set the boat and then turn works really well
The 4PM is a great value for all the functions it has.
Probably the best radio for the money in the Futaba
line up, unless you want to ante up for the 7PX or 10PX.
The PV is really a good first entry radio.