Well, I don't see why they wouldn't work, but I also don't see why they would be necessary in a normal fishtank. Maybe if you had a bare-bottom tank with no decorations it would be wise to have something like that, but most tanks with gravel, plants, decorations, etc. have plenty of surface area for bacteria to adhere to... besides, a fake plant is going to be cheaper and more attractive than a device like that ever would be, IMO....
Others may have different opinions, but I'll stick to tank deco as a biological farm, thanx....