yeah, while some exercises are worth the time, sprinting is clearly superior, try it on an incline next time, not only is it safer (less chance of face planting) it's more physically demanding so in my opinion it's better all around. It also makes you lightning fast when sprinting on flat ground. It's basically the same thing as doing weighted movements, then doing those without weights.
Though I don't sprint as much as I should, I believe it's a great fat loss tool when not over-done, the 1x/week Mark recommends is just right.
As far as post workout, I can't eat immediately after, I like to wait at the very least an hour, but since I do it in the mornings I actually end up waiting maybe 3-4 hours and just eat lunch as per usual. It's probably a good time to have a high carb/low fat meal though. Edit: Forgot to mention that you SHOULD wait at least an hour to allow the HGH to do it's thing, that is: burn fat and promote muscle growth and then eat. Eating right away causes insulin release and all the HGH goes away. If you're using sprinting as a fat loss tool primarily, you want to wait at least an hour before eating anything.