Wow - what a clever and well-designed protective cover. Little, but powerful magnets strategically located, locks the cover in place when using it as a stand (vertical or horizontal) as well as holding the tablet in place. There's even a little magnet which activates a little switch which put the table to sleep when you close it. Clever!
Another really cool feature is that you can slide the tablet up to use the rear camera and it locks into place. Again, all done really well using magnets.
Quality is really good too. Hard plastic back covered in top quality leather. Soft protective cloth inside to protect screen.
Not cheap but worth the price.
The only downside (unavoidable) is the added weight. The svelte HDX 8.9 goes from being crazy light to feeling like it has substantial heft.