This is lame.
I understand the merit of putting Freeza on the team from a writing perspective, because uneasy alliance setups like this can be interesting if done skillfully.
But if it really turns out the switcharoo sticks and isn't just a gag episode, this is one seriously clumsy way to implement it. It's a profoundly stupid marketing move to take Buu, who up til now really wasn't given anything to do in this new series and who people were waiting for, and dedicate several scenes to building hype for his return to relevancy, only to unceremoniously deflate all of that again and kick him off the roster. Using the same tired excuse that has been used twice before already, no less.
I don't really consider myself a Buu fan; My approach to the character is pretty much take it or leave it. But I feel for those who are, and who had their hopes built up to see more of him, only to get shafted yet again.
As for his replacement: It kind of makes me roll my eyes. I feel like the Freeza thing has been played out. He's had his arc/movie and they kind of failed to do anything interesting with him, probably because there WAS nothing substantial left to do with him. I think his story was concluded after Trunks cut him into ribbons. The only interesting thing left would have been for Vegeta to get the kill and thus closure for his own past. But then they didn't do that either, so... I don't see what yet another return will accomplish.
In terms of battle spectacle, Freeza is kind of... boring. Most of the intrigue of him as a villain came from his role in Goku and Vegeta's backstory, his sadistic personality, and the fact that he was on an entirely new scale of power that seemed absolutely insurmountable at the time. In terms of skill set though, Freeza is actually pretty vanilla. He's strong and he uses ki blasts. That's it. That's a rather hefty step down from Buu's set of weird abilities like absorption, transformation, being a weird blobmonster, etc.. To say nothing of other villains and what they could have brought to the table.
So yeah, rather eyebrow-raising move there on Toriyama's part. But he's known to enjoy messing with people, so it might be intentional.