I have 5 WE GBBR's G36 , 2 M4 based L119's , L85 and G3 and cant say I've had any issues with any of them. The 119's in particular get used pretty much every game day and all year round. I also have the Umarex MP7 which a cracking little beast and unlike the tm one actual size.
They all get properly serviced after games , the WE's have NPAS fitted along with maple leaf rubbers and Omega nubs .
As others have said play style is different. I love the sneaking up and picking my shots style of play. Generally I run 4 or 5 mags and a speed loader for a game.