Question is how you get people who aren’t seeing large price increases to join such an app. It’s easy to imagine a world where only the people above the mean in inflation search something like that out, giving off a false impression of numbers being cooked by institutions that use more complete methods.
Just have to add a bit of value in some way. For example, if I could just take a picture of my receipt after shopping, and a 'budget' is filled out for me automatically, so I can track my spending, I'd use the hell out of that.
Doesn't have to be much if a value add. Just something.