I have SS-Tronix on all my trailers so everything is fully interchangeable. It's a great system and I'm really happy with it. I agree it's quite pricey, but if you look at the hardware and all the R&D those guys have done I think it's still good value. It also means that I can activate additional servos on 2 of my trailers (coupler for the road train and ESC for my tipper), because the system allows for transmission of signals for 1 servo channel on the trailer. I bought the kits in stages as I got the truck and trailer kits so the $$$ was a little less painful but if you're looking to do all your fleet in one hit
I would suggest contacting Scott and asking for a bulk deal.
The key advantage with SS-Tronix is that it uses a line-of-sight IR system between truck and trailer, so that when you uncouple the trailer the signal is no longer transmitted and the trailer is 'de-activated'. With the bluetooth kits, when you de-couple the trailer the receiver unit still picks up the signals from the truck so the brake lights, turn signals etc still operate on the trailer according to what the truck is doing, when the trailer is parked up and the truck is driving around elsewhere....looks really odd!