I am having all my windows replaced this week. Happy for you to pop and have a look if you want.
I did an extensive research as I wanted to make sure I made the right investment. Ayrton seems to be NV's little "chouchou", and as Annabel always mention him they get an amazing PR.
Now it depends if you look for cheap or for quality, but I wanted quality and decided on Accoya wood. The wood is key to the windows. Ayrton don't do Acoya wood. So I had quotes from others who did them and it would be too long to explain why but we decided to gowith http://www.londonboxsash.com/
and are utterly happy with our new windows.
Now, we shall judge in 5 or 10 years really... but so far the service, efficiency of the staff, cleanliness, the detail on the product, the isolation (we felt it was too hot in the house tonight for the first time in 10 years!) are second to none.