Well, I bought the set and a set of 13's. I didn't buy the 15's or 17's thinking I'd never use them. About a day after I got my set I found the poncho pattern I'd been looking for for a month. It called for size 15's.
I'd order extra cables too. I only got what came with the kit and a set of 60" ones. Well, I had both my 60" cables in use (an afghan for my sister and one for my husband). I realized I'd screwed up my husbands and needed to frog it back a few rows. I wanted to have a 60" cable to thread through the row I wanted to frog back to so I had to scrunch my sisters afghan onto a smaller cable. I think having 2 sets of cables in each size is probably a good idea.
All in all, I totally dig the Options needles. They're great and Knitpick's customer service is awesome.