I can't say I'm too happy with this trade but it really depends on how far apart they were in negotiations (if the Bruins wanted him at all). If he ends up signing a friendly deal somewhere that the Bruins didn't offer I'd be even more upset. I'm not the biggest Frederic fan but even with his inconsistencies, at his age and with the right surrounding cast he is still, to me, a serviceable bottom six forward, and a pretty versatile one at that since he can play all three positions.
So again, this all depends on what he will be signing for in the future - getting a 2nd from St Louis in a weak draft that in all likelihood given the percentage of players picked in that spot won't amount to much, and even if they do will be years out, and a 2026 4th even farther out with less likelihood, the Bruins didn't get much.
I don't hold up much hope for Wanner - a 9th rated prospect on a very weak Oilers defense pool, one in which has added Alec Regula who the Bruins didn't bother keeping.