Derek, it is well worth it.
With the side windows up and the deflector in place you are more cocooned.
As you move forward the air propels over the windscreen then drops to the rear of the vehicle, re-circulates into a vortex and comes up of the floor and is then propeled forward in the cabin, some on youre neck, the rest makes contact with the windscreen and is forced down to the front footwell. Another Vortex and up it comes again to get you.
To me it sort of defeats the object, having the glass roof open is just like travelling in a normal car and hacing the sunroof open, you are not getting the top down driving experience.
I keep mine in the car all the time and whenever the roof is down the deflector is up, you really really wont beiieve how mush of a difference it makes until you try it.
Mine came with the car as it was ex demo, I know they are very expensive to buy from VW
People I know have bought them from ebay from between £93-£150.
Have a look at this link from ebay to see what they have at the moment.
http://shop.ebay.co.uk/?_from=R40&_trksid=m38&_nkw=eos+wind+deflector
I would recommend buying one, you wont regret it.