I was hesitating a bit before buying the extension (the site of the developper often refers to 1.7, 2.5 in the descriptions or menu. And some links are broken as well for example).
Still I did buy the extension and I am *very* happy of the service.
Indeed for some reason the extension would not show up in my backend (blank page). I just sent a email to ARRA and a few hours later my problem was solved and the extension is up and running :-)
Very professional and very kind.
And now I can start playing with the extension & import my hundreds of users...