Summary: I purchased this for my Mid 2011 27" imac so that I could have bluetooth 4.0. I was able to disable the onboard bluetooth and get this to work as the default bluetooth device. For the most part is works fine, although I have had a few times when my iphone doesn't get recognized right away.
Summary: To make it work with a iMac (21.5, Mid 2011) with Yosemite turn off the on board Bluetooth in the system preference and plug in the IOGEAR adapter to a usb port and that's it. It worked for me to connect a guitar pedal (iRig Blueboard) to my Mac.
whew helped with an iMac intermittent Bluetooth board
11 May 2015
Summary: This product brought Bluetooth use on a 2011 iMac that has an intermittent connection. Had to shut off Bluetooth on iMac was the hardest part. As soon as it was switched off this usb Bluetooth adapter was found and stays connected. Saved a trio to a repair shop.
Summary: Some of this product literature says it supports MacOs (manual) some (support site) says it doesn't. My mid 2010 iMac with yosemite saw the adapter and could not activate it somehow. I downloaded kexts, utilities, messed with it for a while but no go. ....I gave it to a friend.