Generally there are two reasons something is sold through infomercials imo.

Either

A.) They're made by someone who has a great idea and is trying to break into a market, and usually pretty good to great quality and have some useful features. They are solid because they haven't been through several cheapening iterations designed to bring down cost while capitalizing on the good name the product held.

B.) They're utter crap that they can't sell in retailers and need someone to hype it up and make it look good because any store that holds them stops after having to process too many returns.

In my experience B is much more common than A and it can be hard to tell which you're getting without looking up reviews before purchasing.