What is "Rubber mulch " like and what are benefits and negatives about putting this under swing set?

I have rubber mulch in my playground area and it looks really nice! It's so much more safe than anything else, and stays put. I have 3 sons and as we all know boys will be boys.... They don't let me breath at all and I can get queit nervious when they're outside playing on the swingset like loonatics!!! Ever since I got Rubber Mulch, I'm so much more calm! They fall all the time and I never hear any complaints! I'm forever thankful to Rubberecycle- thats where I got the mulch from.....