- it's free
- our users tell us it's great having everything in one place (glucose, blood pressure, medication + food tracking) other products often only have 1-2
- we have a diet tracking feature that draws carbohydrate nutritional data from thousands of different types of food
- the UI is very easy to use
- its web based and accessible from any browser (most loggers we found were desktop applications that cost money)
- we are actively improving the service and are very open to listening to our users feedback
As I mentioned in other comments, we don't have any plans to charge money for the site for at least a year. We both have full-time jobs so its not a big priority and our focus now is to build a community around it.