I have two Sanho Colorspace Hyperdrives, each with 500GB drives.
When I travel for more than a week or without my Macbook, this does the job.
I've traveled overseas with these now for three one-month trips shooting my cares 1x then backing-up on each 2x. A cherry-picked selection goes onto the iPad so that I can email my trip's progress and if a client on the road needs me to process quickly or fulfill from my portfolio.
So far, I had one failure (the drive died on the road, but I had both a apart and all the cards) and though it died, I saved the day for a client when he filled his cards and I backed them to this drive which I was still able to recover his files.
The case uses a 2.5 inch drive and my next move may to replace the disk with an SSD for speed and better reliability.
In practice, I'm about to download at least 150-200GB per charge and the built-in reader handles both CF and SD cards. It can be charged with a brick or using a USB mini cable, which also works to transfer files to my system at home. I also have a small AA battery case that will charge the Hyperdrive.
What this has allowed me to do is to not have to pack a computer and all the bulk and weight. Best of all, since I'm not downloading on my computer nightly then fooling with the images, I can socialize or sleep more, though it still takes time nightly with all the charging and peeking on the iPad (now my bottle neck during travel!).
The Hyperdrive fits in my vest pocket and the second goes into my carry-on, so I spread out the risk of loosing my photos. With card capacities rising and cameras taking smaller cards, it's also to the point where you can put in one large card and put all your photos into one basket! Best to back it up and spread out the images, IMO!