I've been invited to use a lounge prior to check-in if I'm early.
It is a very simple proposition.
Ask if it is possible to use the lounge later the same day after check out. If the hotel says "yes," then thank them very much, answer a survey if one comes regarding how they went "above and beyond," and say good things about the hotel.
If the hotel says "no," don't throw a tantrum, don't post on TA, and if everything else was acceptable regarding the stay, thank them.
(If the hotel won't let your friend staying in a separate room use the lounge with you later the same day after check out ...... 
