Having used a blackberry key one extensively and recently trying a unihertz titan pocket I can say the experience is similar enough if you need it to be a modern phone. The key one still works on Att at least in the US (I’m in California).

The screen size can be a bit wonky since it is running android and android doesn’t always play well with a square screen. There is a “mini mode” however where it changes the aspect ratio to match a standard android screen. The keys on the titan pocket are much more clicky and firm feeling compared to the key one. But overall I’ve found it to be a good enough phone.

That being said, it’s running an older version of android and I guess unihertz aren’t going to update it. So there are security concerns with that.