Got it a few weeks back.
It's 'OK' - the authorisation and enablement had to be done at my local MB dealership- their service manager actually installed it and sorted it out with me- no charge.
I say it's 'OK' for what it does it may not be worth it for some folk.
Mine gives me location, parking timer, fuel and battery level and a mileage log, as well as fill up cost (provided you input the price). So quite neat.
Unfortunately my 2014 car set up wont let me have information on the lock status of the car, nor remote locking.
I just had an Autowatch Ghost fitted Friday however which is an untraceable immobiliser so I'm less bothered.
So in summary for me, the £30 ish quid I paid for it is probably worth it
Oh to get it enabled you have to go to the dealership with the V5 and photo ID, just in case you dont pick up on that elsewhere....