From a business standpoint, I'd be concerned about taking a dependency on a web service with the business model I see here. Free for open-source means it will be harder for the company to make money and the harder it is for the company to make money the more likely it is to disappear. If the company disappears, a business taking a dependency on the service is in worse shape than if it bets on a slightly more difficult to implement alternative.

In addition, a large number of non-paying users creates a support load that requires resources that could be used to develop a paying customer base. This also makes it somewhat less likely that the business will be sustainable.

Good luck.