I do not agree:
There are several claims outside on the web of people saying:
"The Jepp license is bound to a tail number"
well - this is only because normally people do not read the license terms carefully. Now, I know that this is NOT true for any license but for the "cockpit mounted panel".
Another story is the sharing - I'm not a lawyer - but be sure that only reading carefully the license terms I have several arguments robust enough for feeling legitimate in doing so :)
Anyway - as Peter said - people do not need that - hopefully out there there are already many who already share the sub expenses. :) (it's just my personal exercise in understanding a little bit better how things work)
If you call customer service and they say it is OK, they can still call you back and say the agent made a mistake
Yes they can but you are entitled to receive such a correction. A company (or a Govt body, etc) cannot give you incorrect information, leave it at that, and then later succeed in a prosecution.
Teo, my honest suggestion (as a lawyer) is just do whatever you want to do but keep a low profile. But of course, you are free to adopt any strategy you like!
Question on a related matter, if I may -
In operations other than charter or regular air transport, can one fly in Europe without "paper" copies of required maps and charts in a cockpit? If the answer to this question is YES, then - how many "independent/separate" electronic carriers/devices are required and what are "minimum" specs (for example, screen sizes) for these devices?
In FAA land there is no actual requirement to have any specific charts paper or otherwise. You just need to be appropriately briefed for a flight which means you would would need to be able to demonstrate that you were. Clearly this requires having reliable access to charts needed for the flight in some way.
I doubt Europe is that simple.
Are European requirements for private flights similar to those described in AC 91-78 - Use of Class 1 or Class 2 Electronic Flight Bag (EFB) ?
In the UK, there is no requirement to carry paper stuff.
AFAIK, there is no existing or proposed EASA requirement to carry paper stuff.
The wording is something like "adequate charts etc for the flight".
EASA will require the carriage of a "journey log".
There may well be a current requirement in some European countries to carry paper, but that should go away under EASA.
So one can fly with purely electronic data. There is no spec on what form that should have.
Whether going totally paperless is wise is another matter 
Obviously I would like to have at least two different platforms for displaying the stuff, and two Ipads won't do that because (e.g.) there could be a PDF rendering bug which will cause both to choke on a particular document.
Obviously I would like to have at least two different platforms for displaying the stuff....
Thus, if you were a Jeppesen user, Peter, you would need at least two separate access "keys" for your two in-flight platforms, plus another "key" for your desktop PC at home, perhaps.
Peter said:
Obviously I would like to have at least two different platforms for displaying the stuff, and two Ipads won't do that because (e.g.) there could be a PDF rendering bug which will cause both to choke on a particular document.
In Australia we have to worry about the termites too .... :)
Thus, if you were a Jeppesen user, Peter, you would need at least two separate access "keys" for your two in-flight platforms, plus another "key" for your desktop PC at home, perhaps.
Maybe that is one reason why Jepp do the four-key system.
I would guess that if you had a bizjet with say 4 pilots, each carrying an Ipad, when the two pilots turn up to fly, you end up with two Ipads in the cockpit.
Interesting point about the home PC. I do know that if you buy say Jeppview 4 (the standard Windows product) you get the IOS (Ipad) JeppTC for only a little extra (and similarly you get an MFD sub for only a little extra). What I don't know is whether that uses up two (or three, respectively) of the four keys.
The "home PC" angle is very relevant because it's the only easy way to print paper copies of the plates. One can print from an Ipad, but the options are quite limited (I am being very polite here, having spent way too much time trying to make it work with non-Airprint printers).
Of course if you have a copy on a PC (or on a laptop, and there is a printer around) then you can just print off two (or whatever) copies of the plates, and you don't need backups for paper The Ipads can then act as EFBs for unplanned diversions.
