I would have to second what HK Ghost said KWA internals in their m4 series hands down I would put up against any aeg.....they are made to last if you dont screw with them. I have upgraded a few things on my sr10.
1- Madbull 425mm 6.03 tbb
2- G&G bucking
3- Madbull M130 spring.
Gun is an absolute beast!
The proprietary hop up is not a great option I will say that plus a few other minor parts that are proprietary also.