Proper o-rings only change the feel in the last 0.5mm or so of travel (providing a softer landing). Any comparisons to rubber domes is a gross exaggeration.
Not really.
Yikes, I just tried o-rings on thick cherry doubleshots and they reduced the key travel noticeably, way more than they do on thin keycaps. Looks like the length of stem left after the o-ring installed is crucial. The longer the keycap stem, the less key travel the o-rings are going to affect. Look at the difference between a KBC Poker "O" key and a Cherry "O" key with the same o-ring installed:
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Cherry doubleshots will need thinner o-rings !