Here is something fundamental you pointed out.
Transactions do not include sensitive informations : it is only informations on how you use your object (some parameters) that will appear on the blockchain, and it will be needed in order to validate its good behavior according to these parameters. Let me explain:
you do have a device that is self-regulating your electricity consumption. Assume it works from 7am to 4pm and your electricity consumption is X. Your friend has a similar device, and wants to make some electricity saving. You can upload your parameters (7am to 4pm), with the formal model your device is running via a transaction. Next all other connected devices can validate your transaction + ensure your friend's device is not compromised with your parameters. This example is quite simple but it can be done with more critical and interesting devices.
This also answer to the second part of you remark: indeed, since all nodes are running light model-checking tools all values in transactions will be verified mathematically. Hence you cannot download parameters that will compromise the behavior of your object.
Moreover all devices will be identified on the blockchain so we can think of a way to ban the attacker's device.
The idea is not to upload private informations, but only informations your device has access to. This is why you need to have a complete control over your device, so you program it using open-source code