No problem, glad to help another fellow Tablo user! The base interface is good to watch and set recordings as I mentioned before with the web to be used for more advanced scheduling and tuner work. The web app is identical to the web app on the OG. That said, most of the missing features are filters for sorting shows, movies, sports, etc. that are in the current Android app.
The Engine doesn't have the capability for connect/outside viewing or setting of recordings. I honestly haven't used the feature on the OG as I live in a rural area outside of a city and have limited internet options and speed, ie... 1 mbps upload.
I can't say much about use with the Fire TV but my OG has been rock-stable for the last two years of use. There were some limited stability issues in the first year as they were continually adding features and improving items. I've always been able to have my unit hardwired as well as the streaming box which helps with the experience. I also switched to a Shield about two years ago from a Roku 3 and that was a big improvement in speed and stability. We still have the Roku hooked up but only use it for one application that is not available on Android TV.
The limited stability issues I've had with the Engine mentioned above haven't created any heartburn with the family to date. Most of the items mentioned have been more of me nitpicking things as they are not perfect yet. I know that they will continually be improving the Engine from what I seen over 3 years of use on the OG. The Engine will be more like the Tivo you came from in terms of response and speed.
Where you already have a 2-tuner do you plan to keep it for a short time period? I don't find myself using ours much except for backup of recordings, pulling recordings with third-party programs, and web viewing on the computer or tablets when the kids are watching other things on the TV.
Let me know what you end up doing as I'm always interested to hear others experiences.