When buying a JG gun my advice is this;
When you buy it, have a reduced power spring fitted. They usually come out the box at 350, so take it down to about 330. That will vastly increase the life of the gearbox without needing fancy parts.
(The stock parts are designed to work well with 350fps, lowering that power will do nothing but good for them)
But otherwise, yeah, brilliant, I swear by them.