I've got the pirahna scraper. It scrapes algae. Added the bladed scraper add-on to it, and I'd recommend that to anyone in a heartbeat. Takes care of coralline buildup likety-split. Never owned the plastic magfloat kind.
If I had it to do again though, I'd probably just go with the Mag-Float. When I bought the Pirahna, I did so because I liked the real wood on the outside part. Thought it looked nicer than the Mag-Float. That was when I thought I would be "storing" it on my tank. Didn't take long before I stopped storing it in the tank, and now it resides on the shelf inside my cabinet - one half on top of the shelf, the other half on the bottom of the shelf! Soo... all the "pretty wood" was just a waste.