We have them here. It's £1 to unlock (you can get subscriptions) and 25p per minute.
Which can add up if you are at traffic lights etc especially on some routes. And it could encourage people to jump lights to save money.
Surely distance would be a better way to charge. Like for taxis.
I know in London that they have a way to ensure people don't pay whilst waiting but this is not so in other places.