This is the new Battlestar Squonker by Smoant. Judging by its size, it’ll probably fit 21700’s but don’t quote me on that. Lots of dual battery regulated squonk mods are about to hit the market, that’s for sure. Stay tuned.
update: It’s a dual 18650 squonker with a maximum output power of 200W and actually it’s not bulky at all. It’s really inexpensive too.