https://www.amazon.com/Amazon-Fire-7-Inch-Tablet-8GB/dp/B00TSUGXKE
This is very solid hardware but absolutely terrible FireOS - it's very laggy, very annoying lock screen ads, unintuitive, did I mentioned laggy? Only good news it's cheap. Normally it's $50, but goes often on sale for $40
Luckily there is a way to fix, but it's not very easy. You could easily permanently damage your tablet and I assume no responsibility. This is what I did and it worked.
Step 1) get this tool:
http://www.rootjunky.com/amazon-fire-5th-gen-supertool/
DL here (not old) -
http://rootjunkysdl.com/files/?dir=Amazon Fire 5th gen/SuperTool
Watch the videos. Make sure NOT to follow advice to downgrade OS to older one - you'll brick your tablet hard.
Step 2) Factory reset/wipe from recovery menu (turn off, press power and volume down)
Step 3) run auto.bat from supertool (unzip it) choose - ADB Driver install
Step 4) Choose Root Amazon Fire (option 6) and follow prompts to run Kingroot and do root - If Kingroot fails (mine didn't) - reboot and try again.
It must succeed. this is showstopper.
Step 5) Install Google Play store and install flashfire 0.53 (or just google and install it from apk mirror site)
Step 6) From here follow steps here:
http://forum.xda-developers.com/amazon-fire/orig-development/rom-cm-12-1-2015-11-15-t3249416
Look for "Fresh Installation from FlashFire 0.50"
Make sure to download CM and Gapps zips prior:
CM:
https://www.androidfilehost.com/?fid=457095661767103103
Gapps:
http://opengapps.org/ (Select ARM (not ARM64) platform, Android: 5.1 and Variant: Nano)
End result: It's running CyanogenMod 12.1 which is practically tastefully and lightly modified, a stock Android Lollipop 5.1.1 OS. It's much, much smoother running and it's a pleasure to use now.
Things I done after install is to enable back root - it's a simple toggle in dev options.
Installed
https://f-droid.org/ and from it AdAway app. Both require root as second one blocks ads for all android apps, not just the browser.