In terms of their ability, guys like Hairston, Keppinger, and Freel add a great deal to a team. They don't cost a fortune. They have the basic talent to provide a good performance. They hustle. They're versatile. And they are necessary because everybody can't be a $10 plus million superstar.
I have no doubt that Hairston will continue to perform well, he does not look like a flash in the pan to me. Similarly, I always thought that Freel added a lot (despite some errors of aggression). Freel plays hard and, in streaks, can hit. He plays multiple positions including a reasonable centerfield.
The Reds' failure with Freel was not overestimating his talents, but being too optimistic about his ability to stay healthy. He was a major injury risk and that was the flaw with his deal. Hairston seems to be a similar injury risk. He's been hurt much in recent years and probably can't be counted on for a lot of games.
The big issue with these guys is the injury risk, not performance, IMO.