I purchased this to go with my Macbook Pro because, being an early `09 model, it did not have an SD reader. With the new updated drivers for OS X Lion (dated 16th August 2011) this now works - and very well. The card is secured with a good click. I have only tested this with an SDHC card, so haven't seen how quickly it can run, but it seemed to max out the promised performance of my SanDisk card.
Do be aware that you need drivers for this to work and that these are not included with the product (searching for 'Transcend SDXC' will point you in the right direction).
Oh - and for those of you using Macs you get a new little icon in your menu bar that you can drag off with a CMD-click.