the frame is the same just more gears from the looks of it. jack has less gears but is lighter and a bit better on the components.

as for someone suggesting the birdy for off road i think that's only good for light gravel because the shocks are just small travel and good for road bumps. Plus their choice of tires being 18" is very limited compared to 20" sizes. also the lowest end birdy can buy you two brand new jacks, so the price range is really up there.