For many decades, I have never had an allen wrench break. Bend, yes, but never snap.
But yesterday, in trying to remove a reluctant wood(!) screw, I had an 1/8th inch allen wrench snap, and I wasn't even using a "cheater." Poked a hole in my finger, it did.
The particular allen wrench, from a company who shall remain nameless (Task Force - Lowes house brand), just smooth broke!
I went out to the truck and retrieved my traveling allen wrench set (I think the set cost about three bucks from Harbor Freight) and removed the target screw with no problem.
Analysis: The problem wrench was part of an eight-wrench set configured in sort of a Swiss Army Knife rendition. You "open" the desired wrench and twist away. The long end of each wrench is formed into a loop so that it can be attached to a small shaft on the "knife."
I suspect that the annealing process necessary to form the loop made the steel more brittle than an allen wrench should be, and that's the reason the wrench failed.
Whatever the cause, I plan to see whether Lowe's has a lifetime guarantee on hand tools - like Harbor Freight - or whether in that regard their tools are likewise inferior.