I can only add that for me, in Germany, with either Vodadone or T-Mobile as the carrier (the third of three German carriers, Telefónica/O2, may be a different story, I have no such SIM card to try), the device is usable for both telephony and mobile internet access with some but no too severe connectivity issues, at least since I've been running the LTE Discovery app in "No-LTE cycle" mode.
(Until I installed LTE Discovery I used to carry a mobile Wifi router with VoWifi enabled on the phone, which I still sometimes do and which of course makes for an even better and actually quite perfec