There are pro's and con's to either roof or tow bar mounts...
ROOF RACK:-
Pro's...
1/ A 'bonus' of the roof rack is that it can be used for more than just bikes.
(if you remove the bike stand part)
2/ Can be seen occasionally on here For Sale, so can be cheap.
Con's...
1/ Lifting a bike; any bike; no matter how light it may seem at ground level,
up and onto a roof mount can be a bit of a struggle unless you're 6ft tall
as well as being strong enough to balance it above your head/body to
position it onto the rack.
2/ Time taken to 'assemble/fit' all the parts before it can be used....
(Most owners leave them in place, which brings me on to....
3/ Needs extra 'parts' to carry more than one bike !
4/ Greater aerodynamic drag. Fuel consumption rise by up to 10% !
So it's best to remove them when not in use.
5/ Creates extra wind noise...
TOW BAR TYPE:-
Pro's...
1/ Quickly and simply attaches to the tow bar ball.
2/ No need to lift a bike up, over/unto a roof rack.
3/ Can carry more than one bike on the same fitting.
Con's...
1/ A tow bar is not as cheap as a roof rack. Any wiring should be done
by a professional (due to our cars having CANbus electrical system)
so that won't be cheap.
2/ Requires an additonal rear number plate. Original can't be seen
clearly once bike/bikes are fitted to it. The Law states that the
rear number plate must be clearly visible...and illuminated at night.
No big deal as battery LED lights are cheap enough to stick on it.
3/ Unsightly tow bar...unless you buy the Westfalia with removable tow hook.
4/ Won't fit a Brabus...unless you remove the rear splitter !
If anyone is thinking of getting a roof rack type..ensure you get one
specifically for the ForFour (2004-2006). Either OEM or Thule.
Me...I had a tow bar ball mount on a Golt GTI 16v MkII and it was terrific.
I've since had a roof rack mount on one of my ForFours, and my own
choice now would be the 'tow bar' type. But that's just my opinion.