[hannasanarion]

>You would need control of 51% of the nodes to submit a block with arbitrary data and override consensus

This is only true for corrupted miners. That is not an issue in this case because the company controls 100% of miners (and therefore, you are trusting them not to write bad data).

It is completely irrelevant to the question of corrupted clients, which no blockchain can guarantee against. All you have to do is attach some bypassing wires to the input and output of your "blockchain-enabled smart meter" to write completely fraudulent entries to the history that can never be fixed.