They do cool your drive down a bit, I found that the fans burnt out quickly.
I seen a couple of scythe ones that I´d like to try as they have a good rep.
I´m going down this road, a passive HD cooler.
Ive had a hard drive cooler, they arent realy worth it this is because hard drives operate just fine in temperatures up to about 50 C, if your hard drive is getting hotter than that, maybe you should get one
I dont think there is a need to buy such a thing to be honest i find them useless i just use my front intake fans for my HDD cooling and seems to do the trick dont waste you money