It's not that it happens often but I'd rather have the protection if it does happen, as with a riding helmet. I'm sure we've all had horses freak out before. I've had my foot stood on numerous times now before I had any chance to react. Riding many different horses I can't know their individual behaviours.
I don't think that being tired out is going to be an issue, I'm not going to be doing any walking in them.
As for the steel being bent, I'd rather cut off the boot than have a broken foot. The standard that they meet protects against any foot damage with upto 1000kg of weight.