I've seen it done,where the guy had about an inch hairline and his side temple points with the piece on top.
I must admit it looked brilliant, especially the hairline, which if i remember correctly was a FUE transplant.
As for the transition of his hair and the piece i would say that he also had that down to a tee.
He did comment that it was a lot easier wearing as he didn't have any lifting problems to contend with and also styling was a lot easier also,especially at the front.
I myself would go down that route,more so for the sides,using body and head hair but alas i don't have that kind of cash sadly!!!
My advice would be if you have the cash then go for it!!