I like this idea. I would guess a big part of what is making it work for your users is simply the data entry.
This reminds me of something else that I thought is pretty good for combating exercise procrastination also. A little over a month ago I started the "100-day burpee challenge", where you do one burpee (it's an exercise; examples are on Youtube) on the first day, two on the second, until day 100. The important features of this for procrastinators are that it is very cheap to start—you just have to do one burpee—and that at any particular point it is not much more work than you've done before, and at the end you are doing a fair amount of exercise daily.
This will only work if you are the kind of person who can be motivated by the psychological cost of having failed, but still tend to procrastinate. I think that applies to a lot of people though; when I procrastinate, it is usually in part because of risk of failure.