It could be a great stress reliever! I had one a long, long time ago. But, I'd suggest that you go to a gym and get lessons in how to use it. It's easy to hurt joints, etc. unless you know how to throw a punch properly.
The last time I joined a gym they had a boxing ring and I had a lesson. It was fantastic! I agree with Jay that going to a gym and having a lesson or 2 is probably a good idea. I would have kept up with it but it was just too expensive for me at the time.
I used to have a speed ball that I batted around when I was younger... it was pretty fun! Unfortunately the hardware to mount one on the ceiling is not simple and the freestanding ones are enormous so they won't fit in my apartment.