They have 16GB and 32GB, for ten bucks more. Do I need the 32?
It depends on whether you are going to try to store 16Gb of files on that USB Key. The OS they have installed on the USB Key probably only takes up a small portion of the 16Gig in the first chip, leaving the remaining space as extra Disk Space on that key.
The 32Gig version probably just gives you more disk space to store stuff in.
Remember that when you use the USB Key as your Operating System you will not have access to the local disk drives (at least not without risking damaging the data on them), so the only place you will have to store files (photo's, pdf's, programs, etc) will be on that key.
For the extra $10 I think I would get the 32Gig key. That way if you really like it you will have some disk space to grow into for a few years. But it all depends on how important that $10 is to you.