I ride a 2017 model year aluminum Stache built up as a rigid single speed (carbon fork). I ride the hell out of this bike. It has 1000's of miles on it. No cracks at welds or strange things going on whatsoever. I know several people on both the carbon and AL frames (these are all set up geared) and again, no problems.
Unless you crash it or bash it will riding (rock strike, tree branch, or something ride-related) Trek will warranty their frames 100% guaranteed. I had a 2012 year Superfly 100 OCLV that broke three times--1 seat tube delamination, and 2 chainstay fractures. All warrantied without hesitation by Trek.
If you want a Stache, I wouldn't let the rumors of fragility be the reason for not getting one. They aren't fragile. The Stache is one of those bikes that just hit the mark, perfectly.
I am not brand loyal. I purchase stuff based on what I like, not who made it. Of course, the stuff has be engineered correctly and made well. The Stache is just that.
Now remember, all equipment, bikes included, have life spans. Nothing lasts forever. If you buy a bike, any bike, made by anyone, constructed out of any material, it will eventually fail. They all do. Trek is a HUGE company with vast resources. They are one of the few manufacturers who will replace seriously old equipment. Most people won't break their stuff. Most won't ride enough to wear it out. Will you?
