We had competing companies come out and give us estimates. The one higher-end window company told us how crappy Wallside was compared to their product, but their product was almost twice as expensive. We got 7 windows (I think) replaced by Wallside and we have been perfectly happy with them (and have seen a slight reduction in our energy bill, but then the old windows were really crappy).
Wallside did all the windows in the north campus co-ops and royally screwed them up. otoh, they have a generous repair guarantee, and we never called on it because of some bizarre politics with maintenance. But I'd still consider them un-recommended if you can find anyone more promising.