My impression of Viessmann is that they are in fact a quality supplier but with some major drawbacks re open data. They behave very closed source towards their end users. This affects all aspects, from access to planning information down to publishing informations about their bus protocols and data endpoints.
Surely some of this will stem from the fact that uninformed end users can do all sorts of harm to their installation. The same users may then try to open support cases and warranty claims when things stop working.
Another aspect seems to be that Viessmann heavily tries to signal to their craftsmen that they always keep them in the loop. Craftsmen are probably the largest multipliers for Viessmann sales, so they keep them happy at all costs.
Amongst such major goals the group of interested smart home users does not (yet) play any important roll. We are currently negligible compared to their classic user base.
But still: All in all I do not regret my choice of Viessmann for our heating and ventilation systems. They sell good systems with sound engineering. But I admit I had my moments when I started researching about other suppliers and their data politics.
IMHO the current strategy of Viessmann is a rather faint hearted approach towards the future. Thinking publicly of charging for their cloud API without opening a cost free non-cloud option will definitely not convince any smart home users. We need to integrate a dozen suppliers in our homes. I gladly pay €5 a month to Nabu Casa for helping me with this integration nightmare on the top level. But I will not pay to each system supplier in my home. Not to a single one off them actually. Sorry.
