It's so good that if Apple changes the form-factor of the iPad Air, I'll probably take that opportunity to buy the last Smart Keyboard Folio-compatible iPad Air to stretch my use of it as long as possible. (Though I worry that at that point I'll wear out the internal ribbon connectors eventually.)
My wife is still using an older gen 11" iPad Pro and her keyboard folio stopped working (they fall apart after a few years ), so I took a gamble and ordered one. It arrived in the original, sealed packaging. As far as I can tell, it had never been opened, and it is perfect condition and works great. My wife is very happy. I bought a second one for when this one falls apart.
https://www.amazon.com/Apple-Smart-Keyboard-11-inch-iPad-Pro...