Does what it's supposed to do and provides additional USB ports for your Mac.
I've heard that the longevity is a bit suspect but I've been using mine for two months with no issues. I've also read complaints that it can sit at a funny angle on your desk because it's so light. Seriously?
It's also both small and light enough for travel so all in all a very useful and portable product. Keep in mind though that it is NOT man enough to charge your iPad. If you' going to connect it to an iMac, don't bother plugging it into the mains, just plug it in to the back of the iMac and off you go, job done.