My concern about a phone based system is the forced "upgrade" cycle. I don't know how many apps and devices (Fobo Bike, Trakdot, etc.) I've purchased that have been partially or completely broken by the "progress" of technology.
A phone-centric system could, without warning, begin behaving unexpectedly or even stop working due to: OS updates, Carrier OS overlay updates, or even upgrading to a new phone. In order for me to change out any parameters on my Fobo bike, I have to dig my old Galaxy S3 out of a drawer and charge it up. While they can be read by, they don't fully work with anything since the Galaxy S5 came out.
I also wonder how susceptible the system would be to bluejacking.
One aspect of the idea I do like:
There could be a sudden boom market in second hand DEcosse systems!
I'm sure you'll make whatever you go with work reliably, but I'm sure a big fan of dedicated hardware.
