If you punch harder than your average 7 year old, go with the conventional heavy bag. You'll be spending more time picking the up the slam man off the floor after you keep knocking it down with light jabs.
Go with the heavy bag, much cheaper and a lot more durable. As said previously if you hit even with moderate power these things tend to get damaged. In a nutshell heavy bags are like free weights, all types of machines have been invented but nothing beats them.
I got a slam man back when I was 16 years old. I filled it up with sand and was knocking it around like nothing. I weighted whole 150 lbs. About a month later I started noticing breaks and cracks in the foam.. Eventually I knocked the jaw off of it...
i bought a slam man the hard platic type for £300 with the lights on it .... wht a waste of time and money they are pointless, and my m8 had the sponge one and his head came off haha so i would stick to a bag m8
Thanks for all the advice. I guess I'll go with the heavy bag. I think I'll put it on a wall bracket as I don't think my ceiling will be strong enough.
The gym I work at has one of those Slam Man things. They bought the thing about a month ago. Complete waste of money, it's already had half the face torn off and the lights keep failing.