I recently ordered an e² for testing. On the normal level, it is insanely loud, plus a wobbly fan that made unpleasant scratching noises when blowing out. The switching point is always too loud to hear as well. I don't know if I was just unlucky with this particular device or if all e² devices are like this, but devices from this brand are personally unsuitable for me.
I would currently remove the topic of flexible control from the priority list. Something very quiet in continuous operation would be enough for me, but which ventilation is usable? I think that these devices, which only need a round core drill hole, are inherently not as quiet as I would like. Maybe some with a 200mm diameter? Smaller ones definitely have too little throughput, so the fans are loud. I don't believe another manufacturer can be significantly quieter with the same diameter and volumetric flow than my tested device.
Well, currently I have lost interest in this topic, so I probably won't install a decentralized controlled residential ventilation system.
