The HD 10 and the Amazon case were on my front porch this morning. First impressions: The setup process is more like an iPad than it used to be. I checked for updates and installed the latest FireOS, then it was off to the races. This thing is way more powerful than my 2015 Fire 7. Apps load very quickly, and there's not a lag when exiting apps before the home screen appears. I didn't see a way to transfer my settings from my old Fire 7, so I had to copy bookmarks, etc., manually, which took a little while.
Just like my Fire 7, the case seems to be very durable, but having it installed makes the tablet significantly heavier and thicker. It weighs over 2 pounds with the case, making it a "hold in your lap" (or on the table) kind of tablet instead of a "hold in your hand" tablet.
I've discovered one annoyance about charging. The HD 10 includes a USB-A to USB-C cable and a 9 watt USB-A charger. It charges at about 1.66 amps using this cable and charger, so roughly the rated capacity. When I tried using any other USB-A charger, the HD 10 would only charge at 1 amp (5 watts). This includes an Apple 12 watt charger, an Aukey 12 watt charger, and a QuickCharge 3.0 compatible charger. Swapping the cable for another A to C cable did not improve this behavior. This isn't a huge concern for me, since I typically charge overnight, but I can see it being an issue for families if a kid is having a meltdown because their tablet's battery is dead. Other reviews note that it will charge at about 16 watts with a standard USB-C charger. Please disregard, I'm not an idiot but apparently my USB ammeter is. ?♂️ The HD 10 charges at 12-13 watts when I don't have a USB test device connected to its charge cable. Given that, I don't think a potential 16 watt USB-C charge rate is worth the trouble or expense of buying a USB-C adapter if, like most people, you have a bunch of 12 watt USB-A adapters lying around.
Overall, I think it's a great deal for $99. I think I will get used to the heft of the case, or just pop it out if I want to use it handheld.