Over the last couple of years I have twice tried to use these guys.
The first time they showed themselves to be completely inept and lost all my paperwork (twice).
I tried again in January (after hearing they had improved) but found that they were still pretty bad (again losing paperwork, not responding to calls and generally having a poor attitude). I have since told them that I'm not interested in their servcies but they continued to hassle me for sometime before I had to tell them where to go.
They're also pretty inflexible and their big selling point (getting you a c.10-15% discount) doesn't mention the fact that new builds are always over-priced and builders will offer discounts if you approach them. The size of the discount is usually larger the earlier in the project you buy the property. I suppose the fact that they have negotiated buy to let mortgage at residential rates is handy, but many lenders (e.g. Northern Rock) will allow you to apply for consent to let on a residential mortgage (once you have it), although this may be a bit of a gamble as they may defer it.
They certainly weren't for me. To be fair to them though, if you can't get back to the UK to hunt for houses, can't be arsed arranging your own mortgage, would have trouble getting a buy to let mortgage, and don't mind shitty service and paying over the odds for fees... then they may be for you.