The difference with the 4G & Bluetooth (Wifi only) models is that with Bluetooth / Wifi you can update the watch data with your smartphone or via Wifi / write SMS or use other functions.

With 4G, you would not need a phone, just an eSIM, so you can make calls / text messages and other functions without necessarily having to have a smartphone with you. Of course, all functions also work with a smartphone, then you could also switch off the watch's mobile data & use it via smartphone, which should increase the battery life of the watch, as it does not have to search for telephone masts.

Unfortunately, I can't answer that. This is the first time I have used such a fitness watch.