Wlan-Watch needs a mobile and its internet access when you are outside. Alternatively, the wifi connection is possible at home - on the other hand, 4g can also work without a mobile phone with an additional eSIM (you have mobile data outside regardless of the mobile phone) ... If anyone knows better, please feel free to correct me.

First of all, the price. And then you need a separate eSIM licence for the watch, which costs extra to the actual SIM card, at least in Germany. In return, you can use the watch to make calls and receive data without a mobile phone.