You can order whatever you want...though your bill will be lower than if you'd also had a meal, you won't be there near as long so the table will turn over quicker & server will have a chance to make it up quicker, so not a big deal. Really, there's people that just order a salad for a meal...just ordering dessert is not really much diff than that!
just an FYI, the Kona Kone is much better to look at than actually eat. The ice cream part is good (think it's all Edy's at Disney) but the rest of it was really, really ~meh~ mostly tasteless (the candy pieces are not real M & M's, bad generic version...cotton candy the pre-packaged variety which is not all that good.) Just so expectations are not too high...
