I've seen them. They work. The components aren't the same quality (thin plastic vs extruded tubes of thicker scratch resistant plastic) of the higher priced skimmers but at <$35 + shipping vs around $200. If you're unlikely to set the unit on the floor and then step on it AND thinking you need a protein skimmer, this would be an inexpensive way to find out.
Thats an old VISITHERM protein skimmer. The whole unit goes inside your tank. You can't get parts for it anymore. It's just not worth buying. you can get a prism proteinskimmer from Big Als online for $89.99.