part of me says sure a BJ is a BJ a mouth is a mouth....
as for ME...
I don't usually blow from just a hummer... the sensation isn't enough. If I was reading a book and someone started at me they'd be at it for a while. I have to mentally engage and enjoy the interactions, and once I give over to the interactions, then I will arrive to the finish line much faster.
That being said, I would think that it would be difficult (but not impossible) for a guy who is straight to mentally go there. That's me. Other guys might have more sensitivity, and might be able to divorce their mental state from the pure sensations. After all, a bj is just a bj.
Again, that's just me.