I saw those flasks the other day at the LBS, but I would like one that is a bit smaller - might have to look at the local drug store and see if they have an alternate squirt bottle that is a bit smaller.
The flasks made for gu are about a 5 or 6 oz bottle with the pull type squirt top on them - sort of like the ones on dish soap bottles. You buy gu by the big container and put it in the flask (although that has GOT to be a messy operation!) that way you can open the top with your teeth and squirt the gu in like that instead of trying to handle packets while you are riding. Sort of like a mini water bottle, but somwhat flattened so you can fit it in a jersey pocket.