We used one in our daughter's crib until she turned a year old.
Likes:
When my daughter rolled into the side of her crib during the night she had a little padding to knock up against. Not much since the mesh is thin, but I suppose it was better than hitting wood directly. My daughter is a thumb-sucker, but if she had a pacifier the mesh may prevent it from always rolling out of the crib at night.
Dislikes:
My biggest dislikes about it is once we got it on the crib it was a pain whenever I had to change the sheets. I suppose all bumpers are like that though. Also, when she started moving around on her own, she could kick a leg up over the bumper and squash it down so her foot still got stuck in the crib slats.
We had to take it out when she turned one because that is when she started to become most curious about the bumper and would pull at it and try and slide it up and down the crib slats.
***Positive note*** If you buy it new, you can resell it on Ebay for almost what you paid for it.