[SR2Z]

I guess this is an old engine, but it's bizarre to me that fuel efficiency could be a factor for something this slow and light.

[saaaaaam]

Presumably carrying fuel on the device was a consideration so greater fuel efficiency helps reduce the amount of petrol you’re lugging around.

[_yb2s]

A major factor if you actually are using it to get anywhere, because it’s likely not practical to carry more than a liter or so of fuel.