The recoil engined AEGs are FULL METAL
so no con there
The only thing i dont like from them is the propietary battery, although you can change connectors and use a regular Lipo.
Mags arepropietary too, but this is due to the fact that these new "SOPMODs" have a bolt stop feature, this is, you run out of BBs, the gun stops shooting until you insert a fresh mag and push the boltcatch. If you dont care about this feature and want to use regular AEG mags, there are several adaptor to make them usable.
This said, it may be more expensive than other AEGs but for features and performance, these are the next step in AEGs and worth every penny.
Gearbox is redesigned and its expected to handle +400FPS with no problem. Recoil takes place in the buffer tube, so it doesnt put stress in the Gearbox
Not all the upgrades are propietary and not only prometheus makes tem, Hornbill in RSOV has gears, nozzles compatible with the gun
I would add "range" to the accuracy statement, a field mate has already done "impossible" kills with his stock sopmod, I havent as im a pretty bad shooter lol
If its your first AEG and are serious to airsoft, go get it, love mine to bits