Anybody who tells you it's balance which determines if a shaft will snap or not is an idiot... it's torsional stress which snaps 'em.. not poor balance.
I and most others are basing our opinion on the posts of those who've had this happen and the word of shops which don't offer larger upgrades anymore due to "reliability issues"... do more research, you've missed a lot. I'm not saying it happens to everyone, but a lot of shops (reputable shops, IMO) kept seeing these come back.