It can break down with any service. If you suddenly find yourself not really getting enough sales any more to justify continuing, if you have a subscription cos

It can break down with any service. If you suddenly find yourself not really getting enough sales any more to justify continuing, if you have a subscription cost you can sit back and let things play out with your current users. Otherwise your footing a monthly payment with no return. Also depends on what type of deal your running, people might be more than happy to pay a subscription given that they know the plug won't be randomly pulled on the service depending on future sales.