Maybe could be called "who wants to win a pound" then

I guess if a million subscribers they could forego the tiny prizes in favor of a big prize for one driver. But I doubt the game is about that if only 9999 points available.
I would also be surprised if there is not a "leave challenge" or "deactivate" button, after joining, especially if not much info given in the app prior to joining. I would join to test it out however it is not available in country I reside.
I found the original press release on Mercedes and Mercedes group websites for above link. You can see in the photos that several challenges can be active at the same time.
Exklusive Einblicke und individuelle Angebote: Erleben Sie mit Mercedes-Benz das Maximum aus digitaler Live-PR. Exclusive insights and individual offers: Experience the maximum of digital live PR with Mercedes-Benz.
media.mercedes-benz.com
Mercedes me Eco Coach: a personal trainer for eco-friendly driving
group-media.mercedes-benz.com