The problem with these services isn't necessarily their ability to evaluate talent; I just don't like the system they use to rank classes. Correct me if I'm wrong, but I don't believe they factor things like what needs a school has, how they managed to fill those needs, what kind of players they filled those particular needs with and, most importantly, how those players fit into the offensive/defensive system they'll be a part of.
They also don't have a scale for judging a player's character, which is so critical in their development once they step foot on campus. All of that factors into how they will perform at the next level. An example of what I'm referring to could be something as simple as receiver's desire to block, or if a running back would be willing to switch over exlusively to linebacker to fill a team need during his senior season. Muschamp and his team have done a great job of filling the needs we have with quality guys.
"I can shoot threes now. I can finesse you. I can dunk on you. I can guard anything, and I'm rebounding better. When I block shots I catch the ball. I can post you up with my back to the basket and hit you with a post move. Or I can face you up and use my quickness to blow by you." - Chris Walker