"Assault bike" IS a brand and it's the best one.
My answer as to why it's effective is "try it".
It's based on the same principle as the rower... the harder you go, the more resistance it provides. And both the arms and legs are involved. When you go hard NOTHING will build up lactic acid as fast and it forces the whole body (legs, core, chest, back, arms, shoulders) to work HARD. When you go hard it's much much harder than the prowler. BUT you can also go easy which is not hard at all which allows you to do intervals and you can go at a moderate pace to work on steady state cardio, always using the whole body.