Schlumpf added new protection rings which made the hubs a little wider. So they won’t fit into common frames without grinding them (the frames) down. There was some manual being shipped with the hub providing guidance how to grind down the frame. Here you can find a copy of that manual.
With the latest batch of hubs that issue seems to be solved. The protection rings are still there, but nevertheless the hubs are smaller again. Just make sure you get a hub with serial number 500 or above.
I am running M0502 in my muni for a couple of weeks now without any issues and without grinding down the frame. I tried with a KH frame, Triton frame, and Surly frame. They all fit. And the hub came without that grind down instructions.
To answer your other questions: no issues at all. My latest Schlumpf hub is doing great (just like the other two older ones do).