Yes you are right! I've seen many small companies here use the "M" or even the non-business "F" (catch-all) visa and that visa was issued with the full knowledg

Yes you are right! I've seen many small companies here use the "M" or even the non-business "F" (catch-all) visa and that visa was issued with the full knowledge of the locals here. No idea about other cities, SZ is in the special economic zone so some rules are more "relaxed". Regarding the entries, yes you need to go in and out every 30-90 days unfortunately.