I don't think there is a "true scoop." Like everything else with horses, some things work well for some people and horses and some don't.
See the other thread a couple posts down on flex trees.
I had a Reinsman flex tree saddle and it hurt my back and wasn't really secure on my horse. No one else seems to report back pain, so I think it just aggravated a back problem I already had. But I do think they are less secure on a round/wide horse than a rigid tree. It was really insecure on my Mustang and I know of a couple other folks with Circle Y flex trees and they seem to have trouble mounting and with the saddle turning if the cinch isn't super tight. But they really like their saddles and that gal that bought my Reinsman loves it too.
I also know a gal who loves Ortho-flexes. It uses a different technology where the panels flex instead of the whole tree. She loves them, but they are pretty pricey.
So it may be worth a try.
I personally have gone back to regular trees.
I think a lot of people turn to flex trees because the saddle they are using doesn't fit their horse properly. (I know that is why I tried a flex tree anyway). But I finally sent a wither tracing to a saddle company, they took an educated guess on the best fit of the trees they had, and what do you know, the saddle I bought fits great! But I went through saddle fitting HELL before I found the right saddle.