Yes they work fine. I set up a network for the first time in July for an orphanage in Mexico. This is our first effort, and I am not an IT person.
We are trying some different tablets, but have 6 kindle fire (kid version). We were looking for something that had a decent warranty and was rugged and affordable.
Essentially, you set up server with a wireless access point. Connect the Kindle fire to the wireless access point in the and then open the Kindle browser (Silk? I think).
You will need the specific URL from the Kolibri server. The documentation walks you through this. I think ours was https:\192.168.1.110:8080. We set up the server to have a static IP address to the wireless access point so that we would not have to change the address on the kindles each time.
I don’t think you need a Kolibri app per se as the browser should be able to do it.
As I said, we just did this in July 2018 so I don’t have a lot of feedback as to how well they are working. We were able to get them to work and connect and run videos. I got one of those “gaming” type wireless access points so in theory, should be able to handle more wireless overhead.
I would have liked to do more “stress testing” with multiple devices simultaneously to see the impact on performance.
I hope that is helpful. I can give you more details if you want to offline.