your pico fan club card has been revoked.
My Pico 21700 arrived about 45 minutes ago and I can confirm it works with 20700 batteries just fine.
The iJoy 20700 will rattle a tiny bit if you shake it hard enough, but doubt it will in normal use.
Oddly, a Vapcell 20700 doesn't rattle. Possibly because it is ever so slightly taller.