I'm a bit sceptical of this comment.

I've probably shown mine to ~30 people and not a single one had motion sickness with any of the "safe" experiences, assuming the device is adjusted properly (IPD). If you stick them on a roller-coaster or a super laggy app as their first experience then yeah that's going to be a problem. But for safe experiences - I think there is a percentage of people who experience disorientation or nausea but it's certainly not half (maybe 10% or so).