You are correct about the circular chain guards not functioning very well. A couple of my bikes don't have any such guard and one does. I still need something to keep my pant cuff away from the mechanism to prevent chain lube stains. The worst case would be getting the cuff caught up in the chain/chainwheel while pedaling. Generally, loose clothing isn't a good idea around moving machinery. A rubber band works fine to control the pant cuff, and commercial clips are also available.