Very reliable actually. You have to drop it off at the terminal and pick it up yourself, but it's cheap and fast. I had an exhaust sent from Pennsylvania to Chicago and it arrived in less than 2 days for about $30.
I've sent through them and packaged the living pizz-monkey out of it. Got there just fine. I had a package sent to me that barely had a cut up box wrapped around it and it was beat to heck. So packaging is key!