IANAAEE (I am not an aeronautical EE?) but from my understanding, the FAA requires stringent testing of their equipment before it's allowed to be used below 10,000, where above, after takeoff and landing it is a bit more lax, on top of slow rule changes by the FAA such as allowing wi-fi to be used (which was likely the result of some lobbying by the industry). Most consumer electronics manufacturers don't want to bother with such testing for under 10k feet use, and even if they did airlines don't want to have to try to determine which are approved and which are not, so just have a blanket 'no electronic devices' policy. Gogo doesn't operate below 10k feet for one, but also, they do go through all that testing that allows them to operate in an aviation environment (they used to be aircell, which made inflight phones and such).
As for bandwidth, the fact of the mater is that domestic flights just are not that long (Gogo only covers domestic flights). Most people I have noticed don't feel inclined to pay $10 for a few hours of internet when they can just read a book, do a little off-line work, watch a movie, etc. That only leaves the hand full of people with an actual need, so it's just good old fashioned supply and demand. I fly between once and 4 times a month depending on work, and have only had to use it once, the speed was fine, certainly enough for the emails I need to do, but also for just browsing once I was done with work.
Security is of course as bad as any other public wi-fi (not very) so use a vpn or whatever usual security you would use.