Well, I wouldn't recommend punching them. They don't have enough swing or give, so all the power your put into your punch is going to travel back to the wrist, elbow and shoulder.
Still, I think they're a wonderful tool for MT training. I've had one in my garage for years to supplement going to train at the gym. I filled it with rubber mulch so it's stiff as hell, but the awkward shape of the rubber pieces allow a little bit of give between them. Really great for working on your kicks, knees and elbows.
I find it strange that a gym would only have pole bags though, I guess as long as there is a good amount of mitt work going on, it's really not a big deal. Sparring drills with another person is going to be the most important thing in the long run anyway.