Umm quick note: the mobile license is per title (game) currently. It's only valid for a single game. Maybe that will change in the future?
I recommend just buying one of the indie licenses for now as you can use them to make & distribute as many games (digitally) for windows, mac, linux, & html5 (free/ad-based) as you like, & you can also export for android/ios with that license (free/for testing purposes), but you will need to purchase a mobile license once you are ready to distribute your game for android &/or ios devices.
Sorry to weigh in on your "buy now" Simon, but I believe that they should have all the information in regards to the non-indie licenses before they splash out money on them.
@pietro-eccher: the general idea is that to begin with you get an indie license. you use that to be able to develop your game & also unlock the export/compile section of the VS editor, once your game is ready you should stagger releases, so you would release for let's say windows, mac, &/or linux first, then wait a couple of months or so then release for mobile devices, which in theory by that point you should probably have enough for a mobile license anyway - providing your game is received well/ok & you are making profit.
Also before I forget, both the mobile & professional licenses include the indie multi-user license with them.