I used to have a major anxiety about being late - an app like this would have sent me into meltdown if used on me. Over time I got over it by the world not ending when friends showed up late - that just gave me more time to read my book.
I do believe that with everyone being connected all the time via cellphone it is polite to tell someone if you think you will be more than 10 minutes late. I equate punctuality with respect, but I know not everybody does.
I do not see this app being particularly useful for anybody.
