They would be good if you were building an electronic load where you expect fan noise. I have some of the 200mm ones I purchased for about ten bucks each after discount and a distro FU. The thickness of the aluminum plate should still give pretty good thermal Z even without a fan. They are definetly hefty so you need solid mounting brackets
Absolutely. A small fan would make a world of difference.
I just tend to mention the potential problem, when this subject raises its head. Many beginners seem unaware of the different types of heat sinks, and how to properly put to use - in particular - the convection cooled type.
It can feel rather frustrating, when you see a well built audio power amp, where the builder has put significant time, money and effort into the project. Yet despite this, then the fine machine ends up burning its way through the floorboards, whenever it has been switched on for a few moments.