I've owned an MK10 and I now own a 1919 Match with the aluminum lower. There is no question the 1919 is the better gun. The derya is fine, but the quality isn't the same. The 1919 match gen 2 with the metal lower is amazing.
My ONLY gripe is that it's not easy to remove the bolt. I haven't noticed it getting crazy dirty around the bolt so it won't have to come out often, and this one point wouldn't convince me to take the derya. The 1919 is worth the extra $$
The Rails on the receiver and handguard are the same height so you can use any iron or flip up sight you want. It has a forward mounted, side charging handle... which works awesome, it accepts regular Comm spec butt stocks, it accepts AR grips and some trigger parts. The chokes it comes with are actually 3 different chokes.
Lots of parts on the 1919 are metal where they are plastic on the Derya as well. The Derya sights are plastic, the stock adapter (fixed AND folding) are both plastic though the buffer tube is metal. The hand guard end cap is plastic.
Biggest problem with my Derya was wear between the upper and lower where the quick release pin held them together. It concerned me. The way the MKA is built, its harder to separate the upper and lower but there will never be ANY wear.
The older MKA models came with a polymer lower (the new one is available that way as well) which I didnt like and is why I bought the Derya in the first place. Now that you can order the 1919 Match with an aluminum lower, it was an easy decision to switch and I have no regrets at all. Only thing the Derya has that the 1919 doesnt is a sweet case. But the gun is more important than the fancy case IMO.