I've used a Jolla phone for almost a year but ditched it because the camera wasn't up to par for me. Besides that I really liked it, pretty good native apps for a lot of things and a fallback to Android that usually worked well enough for things that weren't available on Jolla (banking apps mostly).

The UI looks nice and is smooth and it's easy to SSH into the phone and write your own software in f.e. Python.

If you're really interested try to find a cheap second-hand Jolla phone.