The difference you'll find between good in-ceiling speakers, and in-wall speakers is that the in-ceiling either have provisions to aim the tweeter, or at least have the tweeter mounted at an angle. The in-wall speaker will fire the tweeter straight down.
I wouldn't bother with in-ceiling speakers—it is too much of a design compromise. If I were forced to bother with in-ceiling speakers, I'd get ones designed for the task—to be the least compromised.