It was already said but worth repeating - Fire tablets do not run standard Android, they run a fork and do not have Google Play store, so be sure your app runs on it.
You CAN side load Google Play store pretty easily, but a lot of apps will be buggier on the Fire in general than on true android tablets.
I have an HD10 and had a third gen 8.9" before that. The older 8.9 was more expensive than the newer one but was also faster despite being nearly 2 years older. My new boss just picked up a newest gen HD8 a weeks ago and it seems to be fairly snappy, unlike my HD10 that is 2 years old now, so it seems that even as cheap as they are, they are putting a halfway decent processor in them. He successfully side loaded Google Play store and got all his Google apps loaded on (calendar, hangouts, gmail, etc.) and they work fine, so that was encouraging but don't assume all apps will work right.
If a Fire HD tablet will work for you, it is hands down the best value out there. Either way, I would go cheap over rugged, and just add a case to make it last longer. The ads thing is not even noticeable for me, so I wouldn't bother with the extra $20. Locally our Best Buy usually has them in stock for the same (regular) price as Amazon. At the least you can go try one out if you have one in your area.