Discussion about these from last year -
viewtopic.php?t=355900
Discussion about the Bumblebee there too. As I stated there, I like and occasionally use them, but don't love them. I guess I should try one of these Black Mountains, but I expect that the flatpick blade will be too large for me. But I guess I'll never know if I don't try one.
The other candidate in this area is the Herco Flat Thumbpick -
https://www.amazon.com/Herco-HE113P-Thu ... B0009QTQ32. I resolved 30 years ago that they fit way too loose for me and the blade is way too large for me. I still have a few in my (very large and overflowing) pick drawer, and occasionally try one, which only confirms my view.
If I'm not using finger picks, mostly for guitar or slide guitar, I will sometimes choke up on a Fred Kelly Regular Delrin with my index finger and use it as a flat pick. Pretty tough to do that with finger picks on.

I guess that's where I sometimes find the Bumblebee useful, and this Black Mountain might also be useful. As a hard core guitar flatpicker, I really miss being able to do really strong upstrokes that really require either shoring up with the index finger or a flat thumbpick of the right shape and size that would stick to my thumb like glue.