I've heard it increases 5-10 more points in game from the PR manager. No idea how people predict this, but I've heard it a dozen times.
personally i rate it a bit lower, but Duderino said for me it is more important if i could get a PR Bonus while playing on neutral court.
maybe someone remembers a clear yes or no about it, else i would go for a national Appeal PR and hope that he will work a bit for his money.