I just got a BM551 today, and I've been working the new lock so much the tips of my thumb and index are getting raw
I haven't decided on my favorite way to open and close it yet, though. I can pull the lock with either my thumb or index, but it's a lot easier (especially with sore fingers) to use both, but then I always feel like a mall-ninja when I flip the blade closed that way (or open)
How do you all do it?