ok i purchased this model because of all the DSMR Rx's i have. i had ordered the DX5c previously because of its price and knowing this model was not Marine compatible with my MR's but figured i'd use it for my crawlers and monster trucks. The DX4S the smallest of all my Spek Tx's including the DX3c, which the 4 is going into Horizon Hobby for repairs.
The PRO is the first drop down wheel i've had, truthfully if it wasn't there i'd care less. the screen is the biggest of the others. the balance feels as good as i need, though the trigger feels more like a trigger than the others except it's meant for a smaller finger, my 3 and 4 has more room.
the menu is an absolute book read but intuitive, features beyond a boat unless you have torpedo launchers and trim elevators and moving turrets and water cannons. the plastic housing reminds me of PVC schedule 40 pipe compared to the 5c seems more as .125 schedule, thus part of the price difference, it's just plain noticeable (first thing i noticed holding it) and flicking it with my finger it's more robust. the battery tray you need a 1.5mm Alan (hex) wrench to access it. it's capable of removing the tray and installing a lipo battery instead. i'm going to configure thumb screws for it.
i personally never had a problem with any of my Spek TX's until recently the 4.
i didn't type this to say it's the best and not trying to sell Spektrum to any one, i've read very good about them and i have read horror stories about them. now i own four surface and an air TX DX8, that's just the Spektrums. my birthday is in Oct. i may just purchase the DX6R.
This model was TX only in the box.