Yeah having to pay the whole thing is a little scary. Though from what I heard, unless you have a guarantor in the UK, most landlords would require you to pay 6 months in advance anyways, and there are many scammers out there, and then there are places that don't look anywhere like the pictures (because the pictures were taken 30 years ago when the house was built). With GradPad at least it should be relatively safe.
If I am renting in private sector I would definitely want to check the place out in person before giving them my money, but the problem is from what I heard, it's very hard to find a place to live in August/September, because thousands of other places are looking, too. And if I am going to fly there beforehand just to check out places, I might as well just use the airplane ticket and hotels money to live in GradPad.
Tricky situation...