Well, I'd say it depends on the size of your hands and how you like to hold it. I probably have larger than average hands and find thumb typing to be pretty manageable, while holding the edges of the keyboard with my fingers. If you have small hands, this probably won't work.

To get some idea, you could get a ruler and try doing a 4" reach. If this isn't comfortable, then thumb typing on the keyboard probably won't be, either.

I wouldn't buy this keyboard primarily for thumb typing. It's (barely) big enough for touch typing. Actually, I find touch typing on small keyboards to be an unexpected benefit of the dvorak layout. Because it requires less hand movement, I tend not to have the kinds of issues with losing my placement that seem common complaints of small keyboards.