I've never heard of a cylinder itself breaking. Most people change cylinder's because:
a) they've changed the barrel length of their gun,
b) get a bore-up kit rather than a tighter spring, as they reduce wear on the gears (which IMO are overpriced - $90 more for a kit than a spring - and aren't worth it)
c) want to get greater FPS without using a tighter spring, though I would recommend looking at
http://airsoftcanada.com/showthread.php?t=18038 before doing that
I would stay with the stock CA polycarbonate piston (cheap if they break), as those deepfire ones are shite (had one for less than 2000 rounds before it cracked). Another option is a systema piston, but for the price you could probably replace with a CA one twice over