I've been running them for a couple of years on my JKs. Just took them out this morning. Need to get new ones, but for $25 I'm debating whether it's worth it during winter. Mine were black when I took them out so they definitely stop some junk from coming through.
People should be careful to seat these properly so that they don't get sucked into the lower part of the fan box. Also, be careful not to stress the plastic doors when your arm is in there.
P.S. these were $12 at the dealership and $25 at NAPA last time I checked.