Update for anyone who finds this thread for research.
I just applied my first protective film. It is much more difficult than applying protective glass, because the glass stays firm, while the film is sort of "alive". It bends in the middle downwards as you apply it. There was a very good reason why the company only sells sets of three :-) I chose matte type and it seems to work very nicely.
As for the removal of the film later, I tested it on the protective film that comes with Kobo when you purchase it. A simple adhesive tape you use for paper did not work. But using gorilla (and i am sure any similar tape) did it without a problem just like #frostschutz suggested.
I urge you to be careful when applying either the film or the tape and not apply too much pressure. E-ink display is not LCD! E-ink is much more fragile. So be gentle or be sorry - your choice.
Good luck!
P