Correct, 90 would be straight up and 120 would be 30 degrees behind the shooter. I actually saw a photo of the back of it and it has basically 5 positions - straight, 30, 60, 90 and 120.
Any flash that cannot rotate side to side it pretty much as useless as the built in one imho. At $150 this thing is nearly as expensive as a good 3rd party flash that has way more features and functionality.
Still, I guess if you need a flash that fits in your shirt pocket, like say you are a super spy or something...
A "straight" bounce at 90 degrees off the ceiling is not always the best angle for the light to hit the subject. Depending on the camera/flash position, at 120 degrees one could be bouncing off both the ceiling and wall, and may provide a better lighting "style." It would all depend on the situation.
What would someone use a flash at 120 degrees for?
You can also be shooting at a downward angle (-30 degrees) with flash and bouncing the flash off the ceiling (for example shooting a still life on a table) with flash. You can still bounce directly off the ceiling with the flash head vertical while shooting down on your subject.