After the malfunction was fixed after a few days, the Internet connection has been working smoothly again for a few days. What's noticeable: at least around my place of residence there is either HSDPA (which works great) or GPRS - EDGE is at least not in here. This may be different in other parts of the republic, at least in the south of Fürth you shouldn't force the phone into 2G mode.
Tomorrow there will be another "stress test" in the form of a train ride to Munich - the route is actually useless, at least with o2, as far as the internet is concerned. Let's see if Vodafone did a better job here. Otherwise only T-Mobile would be left, who partly also offer hotspots in ICE's - only one not for the same prices as Fyve offers 😉
The previous parts of this series:
Fyve instead of o2o? A self-test - Part 2: No Internet
Fyve instead of o2o? A self-test - part 1