If you want to be guaranteed to have access to the Aspire Lounge in T5, you should book directly with Aspire.

I understand that lounge fills up quite quickly with all the various access schemes and PP is who they turn away first as opposed to those who have bought day passes directly from them.

They also price match other retailers (at least according to their website) so if you are getting a lower offer from LoungeBuddy they should match.

Here is the Aspire website: https://www.executivelounges.com/air...airport-lounge

Personally I'd rather save the entry fee money and just spend it while camping out in an airport bar or restaurant - but I understand the desire for a lounge. Do note this lounge gets very crowded so it might be a bit less hectic than being in the terminal itself but not considerably.