would this work as SxS card backup
 

In a word... Yes.

There is already a thread on here where someone has reported that it works and is using it.

I have been looking at the 2133 also, mainly due to it's small size. I had purchased an Acer laptop (15 inch screen) and have been using that, but it is too big to be convenient to use when traveling. So the 2133 looks like a great alternative. I'll probably pick one up next month.

There are comments on the page regarding the processor being too slow for media playback, which you may find yourself doing more often.

On a related note, does anybody know anything good or bad about this?:

http://www.newegg.com/Product/Produc...Inc-_-12191024

the good, its cheap.
the bad, it won't work "USB to ExpressCard" you need PC Express not USB

from the Specs on New egg "Important: This adapter only works with USB-based ExpressCard devices. PCI-Express based ExpressCard devices will not be detected. Please check with your device’s manufacturer if you are not certain"