I've been using them for a year now and they're great. I was worried that as they run off the back of the O2 network they'd get second rate data speeds, but that doesn't seem to be the case.
You need to have some credit in your account before you buy a goodybag, so it's not just a tenner a month, there's also a minimum of a fiver upfront cost. You'll also find any premium rate numbers outside of your allowance, so you'll need credit for that too. I've bought a