Took a quick look at them they are a UK registered company, with all the details being on their website and verified:
wck2.companieshouse.gov.uk/0127c4a78be84b62efd9fd5c917a79e7/compdetails

However, it is important to remember that being UK registered even though increasing the chance of their legitimacy it does not guarantee it. Also it definately doesn't guarantee the standard as with any company you are best of trying them out on a small piece of work before placing a large order. Perhaps you could also try putting it through the marking services of another company just to make sure that it is of the correct standard too.

What ever you do make sure you spend plenty of time shopping around. :)