Negatives
In my opinion (only). They are a valuable tool when used with care and a potential disaster when not. The potential for damage is from draging any dry object across the paint; scratches
I've used one for a few months and am very pleased, so far.
The precautions I use are;
1. Only use it for dust, not dirt and mud. If you have these, then wash.
2. Don't apply any pressure. Just put about half of the length of the "strands" in contact with the surface. (don't rest the whole duster on the car).
3. Only wipe in one direction. You may have to wipe an area twice since you're using no pressure, but if it still doesn't come clean, you should be washing.
4. Tap it on your hand after every panel to get rid of any potential scratchers in the fibres.
5. Use it only when its needed. If you can't see any dust, why risk scratching the surface just because you think its been a while since you dusted? Restraint!
6. Follow with QD and a microfibre.
Rarely, you may see what look like micro scratches on dark colors even if you follow the precautions. Relax, these are not swirls, they're just in the wax, and another coat of wax or QD will smooth them out.
They're worth the $, ( but stay away from the water blade; its a trip to the body shop waiting to happen! )