I had a CPR overflow for a year or so, it really served its purpose, but I wouldn't want to use it again since there was a couple of time I woke up thinking it was raining but instead it was my tank over over flowing onto my face.
If you are interested check out this website, super realiable and it will not cause a swimming pool in your place.
http://www.lifereef.com/
Extremely well built.