I recently picked up a Dragy which is a 10hz GPS sensor that can track your performance data. This is pretty cool. BUT the really great part is that you can see the leaderboards by make, comment on other's times (and receive replies). Which can really demystify tuning.
One example of this for me was regarding AMG fuel pumps on non-AMG m278. Madness Motorsports posted that when he went to bigger turbos he had to go with AMG fuel pumps, this caused many to take similar routes. Well the top CLS 550 on the leaderboards ran M157 turbos without the AMG fuel pumps. I was able to ask him and get a reply.
To me that saved a bunch of effort in terms of trying to upgrade my fuel pumps.
There are videos to browse, and it an link to your phone with a mount to take a video. Unfortunately it can also remind you that real life driving isn't always fun. I tracked a 4 minute mile...
The dragy is great as a social tool, a performance metric tool, and in general a highly reccomended purchase at under $150, which is far less than existing popular boxes. These other boxes often do not have the validation feature and the ability to share and track performance with other people.
While I'm not likely going to hard launch my car at this point, the direction it has shown me is invaluable. No AMG fuel pumps, combined with upgraded billet AMG turbos should make the CLS 550 a compelling performance car that can keep up with some of the tuned AMGs.
I would highly recommend downloading the dragy app for free. I also think the box works really well.
Recommended Modification : Put tape over the LED. Way too bright and distracting when driving. Perhaps a few layers of scotch if you want to see it a bit, or electrical tape I'd recommend if you don't need to see the LED.
I've read several places 60-130mph is the new quarter mile. As an owner I feel more comfortable running something running versus launching.