I had a Jelly pro and beside it worked as advertised there has been much bloatware on the phone and the security patches came in really slow - two updates in one year with nearly no new features and with the latest (end of May) update came the Android Jan security patch ...
Bootloader can be unlocked but without any option of a custom ROM ...
The Jelly pro is a cheap little device with cheap components - bought it as small enough backup phone for traveling ... not sure what to expect from a 199,- device with hardware keyboard ...

and the Unihertz support (and website and forum) is a nightmare - besides they ship their hardware bought from their shop very quick and reliable