Thanks for offering the service! The intensity of map tile pricing is always a little baffling to me. For example, with mapbox this month we (got linked to on The Verge and) exceeded the free tier on the 22nd. Two days later and we have a $40 bill and counting, with a week left in the month. We're a free, open source project and can't handle dynamic pricing like this.

My only feedback on your tiles is the lack of POIs. Mostly just bus stops and an occasional supermarket in my area. But I see from the github that this is on the roadmap.