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.
Just my $.02...
Marty