I'll post here because fusion is basically PLO with some minor differences.

Limped pot.
5-way.
Our hand: A8A
Flop: 554r

3 players check to us. Only button to act after us. We probably have the best hand by quite a margin quite often.

Question: Bet or check?

I've never played fusion but I'd bet before someone turns a free 5 in their hand lol

Might be a good spot for a probe/feeler bet, you wouldn't have to go very large to spook out some of the players+you have some additional EQ against 5xx

i have only played fusion a couple times for fun now and i still cant really find the rhythm/game dynamic...so this may be flawed advice

Assume their is a 5 out there, wouldnt personally bet too big, leaves a bigger reraise open, id probably check call to see the action behind,. its 5 way!

Bet. If someone in front of you checked a 5... great, always good to find the fish. There is only one player behind, if one of his 3 cards is a 5 then he will either raise, giving you an easy fold, or call, giving you at least 2 free cards. If someone checkraises, again, it's an easy fold.

If you check you give 4 players two free cards. Yes, you are a long way ahead if no one has a 5 right now. If you check and the turn is anything from 6 - K you might have given someone a pretty disguised full house.

This is not a spot to slow play / under rep IMO. You can only be happy playing a big pot on later streets if you see an A on turn or a cheap river, or if you catch a 5 for your last card and the board brings something unthreatening: of which I can only think of A and 4.

FWIW I would bet slightly more than half pot. Opponents will generally treat this the same as a full pot bet. That is, unless they have seen you bet pot when you flop trips or a full in spots like this.

check it