First off, I am going to start this post off with the statement that these things scare the living crap out of me and I wouldn't ever want to wear one. The concept is, however, an interesting one.
For those unfamiliar with the KTB, the name is short for "Kali's Tooth Bracelet" or "Kali's Teeth Bracelet." The KTB is a simple chastity device that involves a metal ring that is locked around the penis, but the inside of the ring is covered in spikes (ranging from short and dull to long and quite sharp).
The idea is that the ring will be fitted around the penis when it is flaccid. The fit is snug but not tight. If the wearer attempts to remove the ring the skin will bunch up and get pinched by the teeth (possibly causing bleeding depending upon the fit and types of spikes). If the wearer attempts to get an erection, the penis will press against the spikes and cause extreme pain and the penis will immediately return to a flaccid state.
Pretty simple. If you are a guy and reading this you are probably crossing your legs by now. If you are a woman and reading this I have absolutely no clue what kind of reaction you are having to this but I would guess it's probably at some extreme end of "Sweet!" or "HELL NO!" I can say that I read somewhere before that these were out of production for several years due to too many injuries happening.
What strikes me as interesting about something that I would have no desire to partake in is that this is really a different kind of chastity device and it really provides some insight that there are really very different types of Mistresses out there.
You probably already know that the traditional male chastity devices work by holding the penis at an angle or curve and restricting the amount of enlargement that is possible in order to prevent an erection. By encasing the penis it also prevents any form of pleasurable touching. However, it does allow for the penis to TRY to get erect against its confines, leaving the sub in a state of incredible sexual frustration. In most cases, this frustration is the enjoyable part of chastity, heightened awareness of hornyness building to an explosive volcanic orgasm upon release.
This is the key difference of the KTB. Instead of feeding the fires of sexual frustration, it provides a severe negative consequence for even attempting an erection. Rather than preventing orgasms, it conditions in a factor of self-control: the sub shouldn't even try to get hard without permission. I actually think the end result is kind of neat. If you had enough self-control to respond to verbal commands regarding whether or not you have an erection. Aside from Buddhist Monks known for exerting incredible levels of body control, wouldn't subs trained with a KTB pull in a close second?
I would never actually want to wear one of these but I would find it something to be prideful of if you could simply go erect or flaccid whenever ordered to.