Is that installed?? I'm not a fan of the product, but that price is ridiculously low... So low that I would only do that deal if you are not worried about the installer being around to service the product in the future.
At that price it's a pretty sure bet the installer won't be around in the future. In this area Alside charges $80 per sash as a "delivery fee" if there's an issue with the window and the installer isn't around anymore. And they will not just ship it, it must be delivered by them.