I've used BB for years without any trouble. However, I am not saying it is the best. I use other stuff too. Montana X-treme Bore conditioner in my Knight. But in my flinters, only BB simply because I don't like the type of fouling I get when oil and burnt BP mix. You know, that tarry fouling.
My percussions lately I've been experimenting using only T-17. It says it cleans and protects. I am keeping a vigilant eye on my bores to be sure.