The thing that bothers me when this discussion comes up (and keeps coming up, and keeps coming up) is that, let's get real, folks, people often charge their cars for only about a half hour. Or sometimes less. You make your decision to use a supercharger maybe 100 miles away (or there is no decision to make because that's the only available supercharger on your route), and rest assured, things WILL change by the time you get there. Ya think?
This little app (wall sized app) does not tell you the current charge of the car, whether or not the owner is in the car, or what charge the owner wants to be at (which may depend on how good the book is that he's reading). Some superchargers sit a long distance from another, and people going from one to another will want full charge, maybe 2 hours. Or maybe the owner is headed home, we don't know, and only needs 10 minutes.
So this whole idea is not very useful. Driving to the next supercharger and waiting a few minutes is what usually happens. Except on WEEKENDS. If you insist on doing long distance drives on the superchargers' busiest times, you very probably will end up waiting, and knowing that there may or may not be a slot left by the time you get there won't make any difference.
I have driven thousands of long distance miles, and I have had to wait only once. It was on a Saturday afternoon. Imagine!
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As I said, I'm not so sure there is any advantage. This from only about ninety some thousand miles of driving and Supercharging my Model S.