SCAR17 is an amazing carbine, accurate, light weight, very intuitive controls once you have the geiselle trigger, ultra reliable and very controllable due to the design.
For me it boiled down to 3 big factors, the first is the cost to maintain and service it as a hard use work gun with high round counts, that being outrageous, just a field service parts kit retails for $500 so unless your working for uncle sugar it's a very costly weapon to maintain parts wise. The second is the proprietary magazines that are
basically modified FAL mags, again, far costlier than the newest polymer mags like the lancer L7's and PMAG 25rd and not the sturdiest with the baseplates needing to be
taped, at this point I still wouldn't trust any of the aftermarket lowers that accept SR25 mags in a work gun, for a range queen sure. The last factor is the ergonomics, the
SCAR just doesn't have the ergonomic comfort at least for me that an AR10 based platform has and the adjustability to dial it in perfectly, for example I always ran the stock fully collapsed and still would have wanted it shorter while wearing a PC but didn't have the option.
I've had a relationship with PWS for about a year and a half now and it's the only system I run now across the long gun spectrum, this is the newest version of their MK216 which has forged receivers instead of billet making it as light as the SCAR, as I said mine is tuned to 1/2moa which the SCAR could never match out of the box, it takes all measure of SR25 mags including the 25rd PMAG in the picture, cost no more to maintain than my .556 platform carbines and has a vastly lower parts count than the SCAR.
I run everything suppressed so adjustable gas is a necessity for me, this system is as easy as it gets to go from suppressed to unsuppressed in seconds.
PWS's operating system is a different animal to anything else out there and the only AR piston I would ever run, I got my first demo unit about 3 years ago and ran over 20k through it before I decided to go further with them, it's really the only piston system made that doesn't force a tradeoff in some area from direct gas, just benefits.
Take a look on PWS's youtube channel, watch the cutaway video of the system in action, it will explain a lot.