Some of the sales people at retail stores wouldn't know their whatever. They simply get hired off the street and have never actually worked inside a case.
If you shop even further you'll find other adapters besides the one there for seeing a 2.5 installed internally or an external usb type enclosure. There's a large variety of adapters simply due to them being nothing much more then sheet metal with a cable tossed in.
If you see a CompUSA, Staples, Circuit City, Radio Shack, etc. stop in and look over the pc accessories and/or simply ask for one to see they have any in stock.