I think they are. For one thing, we've broken ours literally hundreds of times without any detectable degradation of force requirement.
I was 56 or 57 when that was shot. I've broken my left hand once, but not doing breaks.
It basically boils down to conditioning and technique. If you have good technique and you've conditioned your hands, you should be fine. If you have good technique but have not conditioned yourself, it can be painful.
We did a demo at a local school recently. I did power breaks all day. a series of 8 breaks, all with 8 pavers. My hand didn't hurt at all.
Better technique, more conditioning.