Is there any reason to add binary sensors for the error flags exposed in the grill protocol? How about the temperature offset and min feed rate settings?

I don't think so given that they can be set using the app and since we need the app to get the local key, we can't eliminate it as a dependency.

If there's interest, exposing the error flags as binary sensors would be simple. Exposing the others as sensors would be simple too but we'd need to add services to set them.