They probably charge and then refund it because some people will either not realise they are entitled to a refund, or will simply not bother to collect it, so they make more money.

Don't forget this is the airline that will charge for anything they can think of. Did you read they recently charged a disabled person 20.00 sterling to get him from check in to the gate, because they regarded that as the aiports job not theirs, and the airport in question (Stanstead, London) took the opposite view.

Re the price, it is very cheap indeed but you get what you pay for.