I've had one for a couple of years. I like it because I only have to spend $25 a year to keep the phone minutes topped up (sometimes more if I use more minutes). It does what I want, which is make and receive calls while I am away from the house.
For most everything else it's a struggle, primarily because there is so little documentation available. The user instructions are pretty much "you'll figure it out".
Example - it (Ultra M50G) comes with 8 GB of memory, and I added another 32 (ish) which I configured as internal storage and set as the default storage location. In spite of this, apps get installed in the main, 8 GB, block, and when that gets close to full I can't install anything else. Pre-installed apps cannot be moved to the SD card.
I have a fitness tracker which required an app called "H Band". My wife has a different type that requires "VeryFit Pro". I can't have them both installed at the same time. I have to remove something else first. Having done this I was still unable to pair the tracker to the phone. The Bluetooth was able to see, and pair, with her tracker, but the app was unable to see it until after several reboots. Then, when I selected the device (with a name that in no way indicates it is the fitness tracker), the pairing timed out and took me back to "add a device".
Again, there is no documentation available either for Android 6, the fitness device itself, or the app on what to do when things don't work.
Incidentally, you can't even set the time without pairing to a cell phone.
Any suggestions would be appreciated. My blood pressure is going through the roof. Good thing I have a fitness tracker.