Upload & Sell: On
I haven't used the Zeiss OVF, but I thought the Voigtlander OVF looked like a better trade off in terms of size and cost, so I went that direction.
I have not used the Zeiss yet either. I did just sell my Sony EVF so, at the moment, I will use an older Leica finder I have while I casually look for a great deal on the Zeiss.
I also use the step-downs as a hood as you and others have previously posted. When I used the cheaper, vented hood, I don't recall it being an issue with an optical finder, though I did not use it that way very much at all( so perhaps it was worse than I remember).