I have read that better cross trainer devices offer more flywheel mass with 5kg bare minimum.
Now I have found one offer which tells me there is a flywheel with 9kg having a working mass of 24 kg.
How is that posible?
By adding friction you can increase the effective resistance to significantly higher amounts. It does not feel exactly the same as a heavier flywheel (it slows much faster, for example) but provides effective resistance from a training perspective.