It's legit, I've used it with no hassle at all. I prefer the Starling Card though.
Using these cards you get the mid rate, as opposed to the tourist rate on transactions, you don't pay any fees for cash withdrawals and they are easy to top up.
You get a breakdown of your spending, and I find that's a good way to keep to a budget (wife is not so keen!) It's really easy to top up your card as well.