Checked it out Fri night (5/29)--they were parked outside of Wurstkuche.
An ice cream sandwich will run you $3 ($3.50 if you get it with the edible wrapper, which I did not try).
I tried the Oatmeal Cinnamoneo (oatmeal-raisin cookies with cinnamon ice cream) and it was OK. I can't say it's the best ice cream sandwich I've ever had, but the concept is cute and it was a nice, sweet treat to have after having just eaten a hot dog.
The ice cream was a bit too soft/melted; the cookie was fine... Not much else to say about it.