That heavy bag works OK against kicks, and actually works better sometimes. For example, the side kick is a common one used in sanshou, and is delivered at a slight upward angle to uproot the person (since chest protectors are worn, kicks that move people are preferrable to those that just hurt). The surface works well for this. I dislike it for knees. It has a ring at the bottom so you can bungee it to a base, but with a hard kick it can pull the base even if covered with weights. I kind of like it without the ground attachment, but I have some ideas in the works. Overall, you can kick it, but I find it to be better for punching, foarearm elbows etc. A banana bag is probably a better tool if you really like kicking (my school has some good equipment for kicking, so I don't mind having a specialized punching bag). I've noticed that after lots of work on it, hitting a regular heavy bag feels kind of odd.
Martial arts don't build character; they build characters.