I just registered to ifly, and paid for the one time $66 update. Apparently it's only good for 13 days???
As MDreger pointed out, this update option is geared toward the now-retired, dedicated iFly 700, 520, 720, and 740(b) devices. These devices do not require an active subscription to be usable, though the FAA data they use (charts, navigation data, etc.) will become invalid if not updated. Thus, people who do not fly regularly or are not concerned with the validity of their FAA data may allow their data to go stale and only update rarely. This store option allows for that...it also allows for the iFlyGPS software updates to be downloaded during that one-time update.
But as MDreger also points out, those dedicated hardware devices are no longer being sold, and the iFlyGPS software used on them is no longer being updated. Data updates for those older hardware devices are still being provided, so existing units will remain fully functional with their current capability into the foreseeable future.
iFlyGPS has been replaced by iFlyEFB, which is available on iOS and Android mobile devices and remains actively supported. Mobile devices running iFlyEFB require an active data subscription to be fully-functional, so a one-time update is not appropriate for them.
The website does try to warn users about how this works:
However, if you misunderstood those warnings and made a mistake in your purchase, you should call the Adventure Pilot folks during business hours to ask for help. I'm sure they'll work with you to find a reasonable solution. You can find the phone number on the iFlyEFB Support page,
here.