Yeah, the Airsoft Pro hop-up chamber is a must. The stock hop-up chamber is crap and will start double feeding very quickly, making the gun useless.
Also, if you are going to order from Airsoft Pro, order their reinforced sear, it is also a must. The stock sear is made of soft pot metal and will wear out really fast. And while you are at it, grab the cylinder head, it seals better thus improving FPS and consistency a bit.
http://airsoftpro.cz/eshop/product_i...oducts_id=2231
http://airsoftpro.cz/eshop/product_i...roducts_id=821