I've only had a little bit of time with them so far. This is what StringDog says.
This pick covers all the details. The no-gloss finish offers superior grip. The high-tech Delrin material delivers the snappy response and tone of tortoise shell. But unlike tortoise shell (or celluloid), Black Snappers will not quickly wear out, break, or lose memory.I haven't tried this one playing out, but it seems grippable. But, I'm not sure about tortoise. I have never picked with a tortoise pick, but I've been told in flatpicker forums that the closest you can get to the sound of tortoise without breaking the bank are Clayton Gold picks, which are very similar to (but slightly preferable to) Dunlop Ultex picks. I've played them, and they're hard picks with a hard click to their sound. The StringDog pick feels very much like my Dunlop Gator Grip, with a little bit of a cushion. And they feel thinner than they are. I would've pegged it as a medium, even though it's ever bit of the 1mm that both the Gator and the Ultex are.
These are good picks. They haven't supplanted Claytons and Dunlop Ultex as my favorites, but they are nice picks.