In a typical system, the noise produced by the hard drive is drowned out by a mixture of the CPU fan, the power supply and the various case fans in a system. Far more effect would be gained by replacing your fans with a Vantec Stealth or other various quiet fan solutions. The only time a 7200 rpm drive will produce a noticeable rattle is if your drive cage or support screws are loose.

The cooling effect of moving the drive to a 5 ¼ bay, however, are nowhere near as minimal. The ability to mount an 80mm fan directly below the drive is a large advantage when considering all the data that could be lost if a drive failed from overheating.
The Hard Disk Drive Silencer is solidly built and works as an effective cooling device but seems to be somewhat misplaced in it's marketting as a silencer. It does nothing to reduce the clicks produced by head movement or the typical whir from the spinning disk. It only reduces the rattle that may be produced when the drive powers up and when the drive rocks ever so slightly.

I can see a product like this becoming very useful in the future when exceptionally high rpm drives become the norm. This product is simple to install and simple to dismantle which makes it nice for those with ever changing systems. It would be quite desirable if the ambient noise produced by disk movement itself could be reduced as well.

Pros

- Made out of a very thick solid piece of steel
- Mounting an 80mm fan results in excellent cooling
- Prevents shock during transportation
- Easy to install

Cons

- Should include an extra pad and screw in case of loss
- Silencing effect is minimal on 7200 rpm drives