Seems reasonable that injuries would occur. I don't understand the biomech of it, but one finger pullups is some serious overloading. A tendon injury is probably small to those fanatics - some of those people are nuts - freeclimbers, etc.
If you're going out, go with a reputable company and pay the $. Give them an idea of your fitness level though so you don't wind up in a class with some lardos who can't even hike to the rock.
Good way to meet fit chicks too.