I answered in another thread on this.
They get huge, they are voracious eaters once established, and they are not particularly interesting or attractive as they get larger. Most observers think they are giant freshwater plecos/algae eaters.
I've been bitten by one - not particularly pleasant. Unless you have a several thousand gallon tank (and I was bitten in a several thousand gallon tank) I wouldn't even suggest considering it. at some point it WILL outgrow nearly all hobbyists tanks, even if you have a 250.
They get very large. Truthfully, BIG. Not something to put in most tanks.
They normally attach to larger fish and hang on, in this case they just hang on to the glass.