I don't sell any windows I am retired. I have built manufacturing equipment. done R & D, design and selling of windows, Aluminum clad, all wood, fiberglass and vinyl.
I can appreciate that you haven't had many issues in 20 years but that doesn't automatically mean that what you sell is the best. Also North Star has had a relatively recent redesign that has removed a lot of material from their windows.
You may not have had any complaints regarding air leakage, but the industry air infiltration tests prove that the North Star window leaks a lot more air that others. If you go to the Energy Star web site you can look this up.
http://www.oee.nrcan.gc.ca/residential/ ... cfm?attr=4
North Star = .48 L/S/M squared
Strassburger = .03 L/S/M squared
That's 16x s more air past a North Star window.
Add to this the greater expansion and contraction rate. The Strassburger window will win hands down in a comparison test.
Here are a few things to consider. North Star extrudes from a pellet. This means that the vinyl has already been extruded one time before it is extruded into the window profiles. The main problem with this method is that the additives are slightly evaporated during the second extrusion phase decreasing some of the properties of the vinyl. Many companies do this so that they don't have to store all the different additives, and have the mixing equipment. Another disadvantage is that the extruder (North Star for example) has lost control of the vinyl quality. The big advantage for them is that they only need to inventory the vinyl pellets.
Another thing is that the North Star window has been built with a narrower window sash than most of their competitors. This may offer a narrower mullion when the windows are joined, but the main benefit is for the ER numbers. More glass area means more solar heat gain which goes well with their Hard Coat Low E. The negative is that they are building a weaker window, and if you use U values the window will not perform nearly as well when tested with a soft coat low E