There are benefits to going with traditional brokers who charge an arm and a leg (it can go way over £25). No personal experience myself but if you want to trade small caps they can get you well inside the spread to an extent that someon like Comdirect or IB couldn't. If you're trading size in illiquid shares its probably cheaper to pay more to a decent broker and get them to "work" the order for you.
I also can't imagine Comdirect or IB faxing you details of your holdings whilst you're on holiday (which proper brokers will).
wysi