we've got several of them....for the price they're great, but should only be used for tanks 3 gallons and under. as for doubling up in a 5g, i wouldn't, just because of socket wastage. if you don't mind using two outlets to do what one could, then go for it, but you can buy a stronger heater for just a few dollars more than two bettastiks would cost, so i personally would go that route, and have an extra outlet to use.
by the way, go ahead and buy them from AllPet....they're selling them for half of what amazon's charging.
Last edited by homegrown terror; 12-17-2012 at 12:10 AM.