We picked Windowtech mainly for their installation warranty and good marks on this site. So far, we are happy with their services - they installed a big main window (109x64") on our ground floor, and fixed the small one in our washroom. Their sales rep was very curteous and professional, good in communication and addressing our needs. Price was competitive. I was not there when istallation was done, but my family members who attended told me that the crew came and carefully did all the job, including the cleanup afterwards. Current experiences make me confident that the window will last us for many many years.
Why did I give it 9 then, instead of 10? Mostly due to grills inside our windows. At the close range, they show that they are all built out of pieces (you see all the seams, and it looks a bit cheap therefore). Also, the distance of vertical grills from the sash on the middle glass is slightly larger than those on the side glass. None of it is really a big deal, and is not noticeable at casual look, but while first issue could be common to all windows due to the way grills are done today, the second issue could have been avoided with a tad more effort, or thinking, back at the factory. So, when designing your window, pay attention even to those minor details - I am sure that Windowtech will do its best to accomodate you.