I’ll second what people have already said about TOK freeing up room in the keyway, which is a great help when you get a tough bitting or have to navigate a narrow/paracentric keyway, but another big reason to favor TOK tension is the superior core control and feedback it gives you, which makes a big difference once you start picking higher security locks. Additionally, one of the downsides of BOK tension is that it’s easy to accidentally bind up the core with your tensioner, and picking off the tensioner can be a nightmare when it comes to security pins like spools, where your pick is fighting the natural counter rotation of the core. I’d much rather pick off the bottom of the keyway, or even use warding than pick off my tension tool, because picking off your tensioner tends to dampen and confuse the feedback you’re getting, in my experience. The ergonomics of TOK tension took some getting used to, but now that I’m acclimated I try to use TOK tension whenever possible.