Hi
Welcome to the world of Airsofting and these here good forums
The weapons you have mentioned are both very good as G&G Makes some very good internals, the differences between the two weapons (bar aesthetics) is as you mentioned the blowback system used by G&G as a feature.
G&Gs blowback system for the gearbox is a simple pneumatic system, some people like them, some don't as it adds complications to the gearbox but not by much IMO.
The difference between the actual gearboxes is that the blowback one has a port hole on the top of the gearbox, the cylinder has a hole to match this, there is an additional cylinder on top of the gearbox which has a small spring loaded piston inside it and this is attached to the bolt plate. When you shoot pressure from the main piston ports some air to the small piston which pushes back the bolt slide, the spring in the small piston then returns this back to the normal place. The video below gives a good idea on how this works:
https://www.youtube.com/watch?v=yyeGfob0ZUI
Its more of an aesthetic appeal and i like it, i have a TR4-18 and have kept it plus it looks cool with the slide bolt moving back and forth in head cam vids.
The rest of the gearbox is the same, high quality gears, piston with AOE set etc.
Though i have found G&G safety levers on their version 2 gearboxes occasionally slip so you could shoot whilst the safety was apparently "ON", my MP5 had this problem but so far my TR4-18 hasn't had it.
Lastly whether you do or don't, if your gun is supplied with a built in MOSFET made by G&G either use NiMh batteries or restrict your use only to 7.4 LiPos as it does not like 11.1 Lipos contrary to what the supplied paperwork says, if you do want to use an 11.1 lipo for the Rate of Fire then change the MOSFET.
Hope all the above helps and again welcome to Airsoft
