We had an excellent overall experience getting fiberglass replacement windows from them. The estimate consult was markety, but professional. I don't think we could have asked for more in terms of installation, though. The crew was punctual, professional, and friendly. They replaced 13 windows in about a day and a half, and left our house as clean as it was before they started.
We have marble window sills. They broke one on the first day, and immediately told us about it. They brought a new matching sill the next day and installed it. It matches perfectly. Mistakes happen, and how a company handles them is often very telling. Kudos to Thermo Twin for handling this so well.
The windows are of much higher quality than what we had before (older aluminum). We'll see how they hold up and affect our energy usage over time, but for now, we're very happy with our new windows and with Thermo Twin.