The cage or the cock?
And no, neither should break, unless you buy a crappy knock off CB-6000 from China which will split and give you the most painful pinch you can imagine in the middle of the night (trust me, the screams woke me…).
And while I’m not a doctor, no, I don’t think your penis can’t ‘break’ being in a cage. It just can’t get hard in the first place. Penis injuries happen when your cock is hard and you mishandle it (apparently) but stopping them getting hard in the first place doesn’t seem to be a problem.
However a TIGHT fitting is important, as you want to stop the erection before it gets momentum. So that’s why, unless you have a really big willy, I recommend the CB-6000S (S for small) as your first exploration of chastity devices. And remember, if you follow that link, which is to Lovehoney, our favourite toy store, they have a year long no questions asked return policy. So try the small one first, and if it’s no good, send it back and upgrade to the CB-6000 or The Curve versions!