I use two of these, one on each radiator input line.  Do they help?  Can't say for sure or how much, I have no hard temperature data to prove or disprove.  What I can say is I have no, zero overheating or boilover issues in ANY terrain, and I run guards not louvers.  Hard racing, slower going with my kids, tight NJ pines at a walking pace, or clawing up a rock covered mountain trail is all good.  I think that they must help, and there is no downside, so I will move them over to the '12 and ditch the thermostat.