I've never played with safewords, and don't think I ever will. For some reason the idea never sat well with me, and I hadn't stopped to think about it until I started Doming more recently.
Growing into a kinky mindset so early in life, I learned about my own personal interests before I was exposed to BDSM lifetsyle as an adult. Trust was never an issue to me because I truly didn't know any other way to approach people. Call me naive, but I simply haven't seen - and won't believe - that a notable portion of people would truly violate someone's trust.
The fact of the matter is if your vetting process fails and you meet one of the bad ones, nothing is going to save you from that mistake. Violating trust is violating trust is violating trust; safewords do not have some magic immunity to this fact. If someone has no problem violating your trust, there's nothing to stop them from disregarding the safe word. Rather than potentially allowing yourself to be lulled into complacency by a supposed failsafe, focusing on whether or not someone is capable of reading signals and responding accordingly is a far safer approach.
On top of the safety-oriented pratfalls of using safewords, they can get in the way of scenes designed to be more intense. Depending on how difficult a boy is to train, punishment can need to be intense enough to leave a lasting impression and allowing a safeword puts a cap on how intensely a boy can be punished. Of course there's always a concern for safety, but any Dom worth his salt should be able to tell the difference between an "I don't think I can handle this" howl and a "I just broke my wrist" howl.
The best thing I could say regarding this is, using a safeword in some instances can be like trying to run before you can crawl. If your trust in a guy is so fickle that you think he can't read you and you need a failsafe, it may be wise to experiment in some lighter forms of play with him; maybe try a basic hogtie with some spanking before letting him sleepsack you and beat your balls.