It usually gets very poor reviews. It works better in a sump than hang on. I had one on my 40g for over a year and just replaced it with the Coralife Superskimmer 65 earlier this week. I can tell already that the Coralife is a MUCH better skimmer.
That said, if it's for a small tank and you're going to keep stuff that doesn't need super clean water (softies, mushrooms, zoanthids, etc.) the Seaclone might be adequate.
Mariner