All good advice above. Your best bet will be to contact the manufacturers directly and ask for the names of a dealer or two in your area...
I'll just add one last comment RE:
Should I be concerned that they primarily use this window brand? Thanks.
That in itself may or may not be cause for concern. Certainly the most knowledgeable and quality focused professionals are going to insist on using high-end products, however using a lower tiered offering could be an indicator of "cost-cutting" which could extend to the installation realm as well, but it could also simply be a high-quality craftsman that just isn't a window nerd
and really doesn't know any better.