I used mobile ordering on two trips this year. The first was in July and it was only available at Satuli Canteen. I hit a not-too-busy time, but I wanted to try out the mobile ordering anyway. I put in my order and as I was walking up to the restaurant, I submit my order to be prepared. I walked in the doors and asked a CM if I could find a table while my mobile order was getting ready. She told me "Of course", and as she moved the rope out of my way, my phone dinged that my order was ready! I did it again later that evening at Satuli Canteen again (wanted to try both desserts), and it was just as quick.
We went back in October and it was not as great. I submit my order after I dropped DD off at FoP and decided to just wait outside Satuli Canteen until I got my notification. I waited a few minutes and decided to go inside and check on my order. I walked up to the counter, and my meal was sitting there, but the dessert wasn't on the tray yet. A CM came up to me and asked if I needed anything and I told her that I thought that was my order. She looked at the name and confirmed it was my order and told me it was all set. I told her it was missing the dessert. She looked perplexed, and walked away. She turned around and told me "You still need your dessert". She grabbed it from the cooler and set it on my tray and walked away. I was befuddled a little. Very similar experience half an hour later and Flame Tree, not nearly as fast and somehow confusing. But, both times it was still quicker than the regular line (and it wasn't too busy)! I will definitely utilize the option in the future, hopefully they'll get all the bugs worked out.