I think it’s a great idea to utilize what would otherwise be a waste product. The composite frame is covered on the inside with a real wood veneer that is stainable. It looks like real wood except for the shape of the corners, which are curved in a way that solid wood seldom, if ever, is. The outside is covered with a thin skin of fiberglass-like material.
It seems to me that the downside of a window like this is twofold. One potential problem is that the veneer on the inside could peel, especially if it gets wet repeatedly from moisture condensing on the glass and dripping in cold weather.
The other potential problem is on the outside. There are seams in the protective skin at the corners. Caulking seals the seams. If the caulking fails even slightly, water can get in and be absorbed by the composite. Then it will swell, making the leak worse. Eventually the window is ruined.
If I had windows like this, I would check the integrity of the caulking every year. Also, I would make sure no moisture condensed on the windows in the winter.
Solid wood windows are susceptible to condensation dripping in the winter too. If the finish is ruined they can be sanded down and refinished with no danger of veneer coming loose. Wood windows are available with an extruded aluminum exterior, which prevents water from ever reaching the wood frame.