I logged into the app with user A and then log out. Then tried to login with B - it prompted me the credentials in the web and redirects me to the app but now with details for user A. Looks like some caching issue.
ON the "My Account" tab on the app, sometime I see a one-line json code saying {"login": "invalid code"} or something like that ( I don't have it now).
Sometime the offer are only valid for new activation. Otherwise, generally there are no hidden things. Some plan have on "reduced rate" dare after the cap is reached, some plans do. i guess the above plan has no such reduced-rate data after 20G is re...