Originally Posted by Novalite

It's rather normal that the crank arm broke before the extender, given same or bigger extender strength, the forces momentum increases with the distance and the extender moves the crank to a bigger distance - a pedal extender increases the momentum already by its presence, or put in other words: for a given force it can make a crank arm break when it wouldn't have broken without the extender. Or put in yet other words: maybe it could make sense to make the extender only just as strong as the crank/its pedal eye since stronger is useless and if economics are taken into account, more costly for no gain, on top of a crank replacement that may (likely) cost more than an extender replacement.