Grown from seed do you mean?

Poincianas tend to flower better after going through a warm dry season. On properties those planted in full sun well away from gardens where they never get irrigation do best. I'd think that in pots you wouldn't get good results. I've never tried though but you never really know for sure unless you've tried.

They are all grown from seed

I've read they can take up to 10 years from seed to flower.... advanced trees grown in bags, or grown in-ground and dug up for relocation, would be about that age. However I think they would make excellent bonsai plants if only for the attractive shape and leaves.

They're listed as one of the world's 5 most beautiful trees. I doubt they'd take well to bonsai culture. Might be worth a try though, if you have years of patience.