I have one I bought about 1 -2 years ago. I like it works well, and I like the tracking on the website. If you have a paid profile on Brewfather it will integrates with that as well.
Like to keep track of my batches, and be able to come back later to review. For battery life I think I have three batches done since the last charge, is floating in beer now and says 86% battery life left. That is with changing it send data every 15 Min(default is once an hour). I like that it will send information to the cloud via wifi without any other equipment needed, and the price isn't bad. Only issue is you have to take apart to charge, and then recalibrate once you put back together. Only takes a minute or two to do the recalibration, but still would be nice to not have to do.
As far as under pressure it depends on what you want it to do. Will it get you the correct final gravity? No. Will it allow you to track when fermentation is done and how quickly the gravity is dropping? Yes.
The issue is carbonation in your beer. When you ferment under pressure you will carbonate your beer. Just like your hydrometer this will cause issues for the pill and other floating hydrometers. I have not found a calculator that will adjust for this, but still is better to see the gravity dropping without taking samples, and if you want to know at the end you can take a sample.
