5-speed gear box kit for PX

Hi guys, someone of u can tell me something about this gear kit?

Above all I'm interested about its reliability!

Thank u ;)

i've never used one, but from what i've read the gears are narrower in order to fit in the same space and they wear out much faster then standard gears. i guess racers like them because you can get closer gear ratios in the same gear range and find the sweet spot in the power band easier.