Where it reads "Use tap device":

maybe a little misleading ..
It probably means "Use tap device in tun mode" (Because Android does not support tap mode).
Also, scanning your Router manual we find:
http://www.downloads.netgear.com/files/GDC/D6400/D6400_UM_EN.pdf#G15.201111
Which states:
Note: The modem router does not support iOS or Android VPN client software.
I would contact the relevant websites (Netgear, google play and
colucci-web.it <- good luck with that one) and ask for a clear answer because otherwise it looks like you will be throwing your money away.