MrBoat
I bought one of these units when I got my new Denon x4200w. You mention being unhappy at a product that ran hot. Its not necessarily because of the product but where we PUT the product that can cause heat trapping. Believe it or not, I believe Denon says they want 6 inches of unobstructed top headspace for cooling plus xx inches on the sides. In a lot of shelving, racks and other installs, the receiver isn't getting 6 inches of unobstructed cooling headroom. Many installs are great to look at but bad for heat exhaustion.
I need my new unit to last until the funeral is over, so it has to go quite a while. Someone posted an article about these cooling units and they caught my eye. I had a few budget dollars left over since I went refurbished on the AVR so I decided to get one. I don't necessarily need one, but I do love the idea of running my new all powerful AVR as cool as a slab of marble.
My unit is dead quiet. It looks like part of the AVR: you literally can't see it unless you're looking for it. It does exactly what it says it does: it keeps the heat out and my Denon cool. As far as dust goes : I'm not sure that's any more of an issue with the unit than without it. Dust buildup within the fan unit may occur more often than what would normally build up on the AVR. I don't mind that so much because the fan unit is easily blown out with some canned air. I clean all my electronics occasionally so it would just be one more thing to squirt.
This cooling/fan unit isn't a "need" for me. I got it because it sounded like a cool idea (I love a good pun)