Youll be fine with the single as SJM points out. You dont want a Dual on a 40 Breeder anyway. They are really large. About 16" long from end to end. I got the option with the black internal box. back of my tank is painted black. It blends in really well eventhough it is pretty big even in my 90 gallon. I wouldnt buy another brand personally. Not because they wont work or be as reliable. Some of them are. The LR is simply the best built, definitely overbuilt. I didnt see 200 bucks (for the dual) as an unreasonable expense for something built so well that it will be able to be moved from tank to tank for years to come. Plus the fish room is cramped and it is not uncommon to bump into the overflow and knock it around every once in a while. The peace of mind of knowing it is built so well is also worth every penny for me. If I were on a major budget, I probably would have bought something that cost less. But since I could afford it, it was a no brainer for me. I dont have to spend as much as I can on whatever I buy. Im not like that. But certian important pieces of equipment are worth spending extra to get the better stuff, for me.