Bear in mind that the fire tablets use an old version of webview, which causes problems with some browsers (e.g. fully) and custom components. Also, you can’t disable the lockscreen.
I have just swapped my fire tablets out with Lenovo tab 4s for this reason.
You can search for the program “Amazon Fire Toolbox” to get rid of Amazon ads, get rid of everything Amazon and disable system updates. The program works on most HD8 and HD10 models, at least the recent ones released in 2016-2018. That program is most useful if you want to convert your Fire tablet to an Android-like tablet. The new version also installs Google Assistant, but I don’t know if it is always-on. I would rather rely on a Google Home or a speaker that has better microphones for voiec commands.
What srk23 said, there’s no getting around the old version of Webview (new version is necessary for custom Lovelace cards), except using Google Chrome as the browser for Home Assistant. I also haven’t been able to disable the lockscreen. There aren’t any ads on the lockscreen anymore, but I can’t just press the power button and have it load Home Assistant yet. It stays on the lockscreen until someone swipes up to unlock.
If you configure Firebase Cloud Messaging (FCM) with Home Assistant, you can send notifications to the tablet like any app would do. Or you can create persistent notifications in Home Assistant, so the notification shows up in the HA notifications tab.
I haven’t tried most of these. But the Lenovo is a standard android tablet running a recent android version, and can easily be rooted if required. So if you can’t do it on the Lenovo, you probably can’t do it on any android tablet.
I have mine mounted to the wall with 3m velcro and powered using a cannibalised qi charging pad with a flat connector. Looks neat, and using the fully browser works very well.
I am using the Lenovo pad 4 8. The pad 4 10 is the larger version. Returned versions can be had pretty cheap on eBay.
The connector is a micro usb qi receiver. I removed the connector from the pad and soldered wires to a 5v supply (stepped down from old 12v alarm keypad wiring).
Nice - arrives Thursday! I plan to start by putting it on the wall in the master bedroom and to have it just be informational (i.e. display driveway camera if motion detected, show message when garage opens). I don’t intend to touch it. Hopefully that works.
I second @srk23’s suggestion. I’ve done exactly that to use my fire 7 as an alarm keypad that dynamically displays when one of the doors or windows is left open so I don’t try and arm the alarm if anything was left open.
This is a pic I took before hiding the power cable in the wall:
the power cable is connected to a smart socket, so the table is not always being charged. I have an automation that charges the tablet when its battery drops below 45% and stops charging when it reaches 85%. And I use the front cam as a CCTV
You don’t really need to get rid of the special offers, all it does it display ads on the lock screen. But if the tablet is never locked, you wont have anything annoying.