This is kiosk mode, so it's designed to let merchants place a kiosk in-store in order to decrease lines. It's a restricted version of the full application. You'll have to sign up your business to use the real thing.
1. Items are not grouped together when the same item is added at a later time (or is this a feature?)
2. Updating an order changes the price but not the quantity.
3. When selecting the quantity of an item, there is no visual feedback to let you know what number you have clicked on. It's also not obvious that +10 means 11.
4. Orders that have more than 1 item do not contain bullet points.
See http://i.imgur.com/Onpkb.png for some examples.
This was within 10-20 seconds of playing with it, there are probably many more.
Intelligent display grouping - if the second one added has the same instructions or modifications, group them (but keep them separate in whatever storage area you're using) would be a happy medium, although obviously more work.
I'd suggest allowing grouping of items, allowing groups like 'Drinks', 'Sandwiches', etc. It's somewhat confusing in that example because there doesn't appear to be any sort of order to how the items are laid out. That may make some sense for the actual registers (muscle memory is wonderful thing), but if the customer is expected to use that interface themselves, I'd expect it to be a bit more friendly.
