I had all of the doors and windows replaced when I moved into this house in 1996. I vowed never again to have to bargain to get the price dropped, starting at eg £10,000 and they could do it for eg £6,000 but I would have to sign up that day. They went out of business shortly after but restarted again with just a minimal name change. I would not touch them with a barge pole. I went locally last year to get one window replaced and it was a very reasonable price, they did not accept negotiations, I agreed the price and the work was excellent. They were recommended by a friend. I think that small and local is best.