I've used the bluegrass real tracks on some of my songs. What I find is that they are usually too fast for me. It's like they are playing "double time". If you slow them down too much, then the quality goes down the tubes. What they do has great playing, but I don't always get the "feel" I want.

You should be able to listen to examples on PgMusic.com. Also, I could send you a short example of what they produce for Old Joe Clark as an MP3. Email me via my website. Might take a couple of days.