I'll first say that my experience with the windcheater is relegated to the Hill People Gear version. Slightly different pocket layout, same fabric. Secondly, I can only compare it to the weight/feel of the Patagonia slingshot, which I owned for a short time.
In my experience, the Windcheater material is more breathable, and on-par weight wise with the slingshot. I've got much more usage-time with the windcheater than with the slingshot, so I can more accurately talk about it's attributes. I've worn the HPG windcheater in temps as low as 20 degrees F, all the way up to 60-70 degrees. Thanks to the breathable fabric and ample pit-zips I was able to make use of it while taking a break during a backpacking trip in the Rockies recently. While I hung my shirt to dry on a bush, I donned with windcheater to give myself a little protection from the sun while I ate lunch. Eventually I got pretty warm, but it wasn't unbearable. Last winter, I used it on a backcountry ski trip and pretty much lived in it for the entire 3 days. I wore a lightweight Patagonia capilene 2 layer underneath, and it was comfortable for me while moving around 20-25 Degrees F. The hood is nice and big and provides excellent protection from the elements. Furthermore the cut of the jacket, including the dropped tail hem, provides a lot of room for layering and movement.
The ambush material seems very durable, and I have every reason to expect that it will hold up to quite a bit of use.
I hope this was informative. Please let me know if there's anything I can add or clarify.
