If I buy a product for which the selling point over others products is that it can be controlled with a free app. And then years later, for no reason at all, you decide that the app will require a subscription to use, let alone at a ridiculous fee like 10 dollars a month for a niche cooking appliance, I would be suing. I don't care what the legalese in the terms of service said. The advertisement and information at the time of purchase should hold true for all existing consumers. If you want to charge new users, or create a new non-free app for future models, or whatever, that is a terrible idea, but your prerogative. But customers that bought the product under the old agreement should be grandfathered to that agreement. If you negatively change the terms of the consumer's use case of your product for profit without any sort of consideration for them, that should be illegal. If it already isn't, I would fight for it to be. That shit is absurd.