The 20mg ones are nic salts which work a bit differently which is why they're stronger. The refillable "freebase juice" is what came in 3, 6, 12mg and it sounds like it's getting banned. Nic salt is supposed to be used at much lower wattage so that you get less with each puff but it works faster (similar to a cigarette). Pretty much all the disposables use nic salts.