Well, I’ve never eaten puffin. I’m not sure taste is predictable.

Except I’d say porgs wouldn’t taste like chicken. Chickens and related birds are odd that their flight muscles are fast-twitch fibers (the white meat) that work explosively for sprints and operate without added oxygen (anaerobic). Fast and furious. But, they need time to recharge after a sprint (recover oxygen and get rid of the lactic acid produced). There is not as much blood flow through the fast-twitch muscles as slow-twitch muscles, which are darker red in appearance (the dark meat). Slow-twitch muscles work for long periods of time and need oxygen from blood flow to keep them operating. So, fast-twitch muscle (white meat) has less blood, and has a more delicate flavor than slow-twitch muscle (dark meat).

Most flying birds have deep red muscle that allows them to fly large distances. They typically taste more like liver than chicken (plus a gamey flavor).

It’s hard to say what a porg’s lifestyle is from the brief clips I’ve seen. But, if they’re supposed to be seabirds and can fly, then they’re probably all slow-twitch muscle, just like real seabirds. Swimming and flying takes constant effort. Living in the ocean means probably eating smaller ocean-going life, which on Earth usually means fish at some level. Many birds that eat mostly fish tend to taste fishy (or so I’ve heard).

So, I would think there’s a good chance porgs would be dense, dark red meat tasting like goose or liver with a gamey and fishy edge.