Personally, for a mill you'd be better spending £93 on CamBam, and saving a couple quid (or 209 if you happen to need a commercial license!).
One thing to note, the hobby license is usually for the previous version. The current commercial packages are on V12, while that hobby offer is for V11, however I don't think there is that much difference between V11 and V12...

As for the main difference between standard and pro, from what I could figure out, it's mainly to do with 3D files. The trail version is only for the standard version, and they're website is pretty rubbish for comparing products (the US site is a lot better).