Just received this gem and I'm happy I made the purchase. First thing you'll notice, is that it does feel very cheap - plastic material, so I'm not sure how long it'll last/whether it can take some serious knocks. The dimensions are 3 3/4 inch long, 2 1/4 inch wide, and just over 1/2 inch thick - it can fit into a moderate sized pocket/bag very easily even with the USB cable.
I've tested it out with an xd card,Pro duo and a M2(mobile), and all work BRILLIANTLY. MS XP automatically recognised the hardware once attached via the USB port and, it comes up as 4 separate drives(G-J), so the only nag is that you'll have to try and remember which drive belongs to which card type etc, but that's just a minor irritation. If you're looking for an inexpensive,portable multi card reader, this does the job.