Is this what I should be getting?

http://www.airsoftmegastore.com/DBoys_Full_Metal_Rifle_Body_For_M4_M16_AEG_Rifle_p/acc-bi-m28-marines.htm I have a JG M16a4. its all plastic but the guy I bought it from put a tight bore and upgraded the gearbox. Am I going to have to get a new hop up? is this going to be a lot of work? is this quality? is this a good deal? Why did I ask all my questions that way? its probably because Im tired.

TL;DR Have jg. want this. what do.