These things are great if you have a hotswap drive cradle and swap out drives a lot. Or if you just have lots of HDDs sitting around. I use these to protect client's original drives after I clone and replace them.

The kits comes with one 2.5" and one 3.5" protector. You can choose between Blue or Black for same price. Free shipping with Prime. Also a great fill item to get up to free shipping if you don't have Prime. Can be found first on the list of "New" Sellers on the links below. They are from Kingwin (the manufacturer) through Amazon. I just ordered 8 kits for $11.92 Shipped w/Prime. I've always thought these were over priced, even though the ones from Kingwin are always cheaper than other manufaturers (some are $10 for one 3.5"). For this price though I think it is a hot deal.

Kingwin HDP-202 2.5 & 3.5-Inch Hard Drive Protection Kit Retail Black SKU: HDP-202

KINGWIN HDP-201 2.5 & 3.5 Inch Hard Drive Protector Kit Retail Blue SKU: HDP-201

Newegg sells them for $3.99 + $2.99 shipping (Egg Saver 4-7 days). I've had these in my wishlist there for over a year and never seen them on sale.
Newegg - KINGWIN HDP-201 2.5" & 3.5" Hard Drive Protector Kit

Meritline sells them for $4.50 shipped.
Meritline - Kingwin 2.5" & 3.5" Silicon Internal Hard Drive Protector Kit, Blue, Model HDP-201