I've tried several cheaper brand brushes ($4-6) out there for cleaning the air vents and dust spots inside the car. This swissvax detail brush does a wonder job on the air vents, does seem pricey but considering the amount of time you'll be using it and how high quality the brush bristles are...it's well worth the extra money spent.

Used this brush on the interior of my Audi S4 and it worked perfectly! The bristles are soft yet firm enough to work the tight areas. Great for working in cleaning product to get the real embedded grime out.