Hawaiian717

I assume they're downloading the whole database each time, not just changes.

Centurion Lounges don't allow nonrev passengers access until they've been issued a seat assignment, and quite often that makes the lounge access useless since seats aren't often assigned until within a few minutes of boarding starting.

Priority Pass lounges don't really have a reason to discriminate against nonrev passengers, since, as far as I know, they get paid by PP the same no matter whether the passenger is confirmed or not. I could see some lounges restricting access to nonrevs when they're busy, but some lounges do that anyway for all PP members.

Priority Pass via Amex Platinum allows access for the cardholder only. $175 for three additional Platinum Cards allows each additional cardholder to get their own PP membership. Each PP member gets in for free, if they bring in a guest under their membership it's $27 per guest.

Priority Pass via Citi Prestige allows access for the member plus immediate family members or two guests. So if the goal is PP membership, Citi Prestige is more attractive since you can bring in guests or family without having to get them additional cards with additional annual fees, or paying per-entry guest fees.

Beyond PP and Centurion Lounges, Amex Platinum also provides access to Airspace Lounges and Delta SkyClubs, the latter only when flying Delta. I don't know Delta's policy on nonrevs using the SkyClub in conjunction with the Platinum Card.