Well the thing is that is one of the conclusions we came too after having built a prototype. I'm not a skinny guy (nor was my partner), we built the thing for personal use and after several months of use we had found that it was simply too much additional effort that a simple meal plan could accomplish on is own. There were several things we didn't account for in our initial design.
1) Battery life on the mobile phone... Keeping your GPS on during waking hours is a big drain in current generation phones
2) People sticking to the plan (ours was designed so that you could go "off plan" if you felt hungry and it would adapt) ... during early testing if you skipped things, it could go out of whack
3) Motivation, we let several people use it, not including ourselves (about 15 all up) and we monitored the use and we found that in almost all cases (except 1) that people just stopped using it after around a month, with it's novelty wearing off after about two weeks. That's when we started to look at how the business models of other Dietary businesses work.
Basically, it had little more than novelty value - a simple meal plan and exercise would have achieved the same result.
(On a personal note, I found it just as easy to ride my exercise bike while watching TV and eating smaller portions to keep losing weight, I just bought smaller plates and glasses to change my perspective of the amount of food I was eating.)