I hooked up to my little belt sander and I also tried it on the Random Orbital. On both tools, hardly any dust around after using them for a about 10 minutes a piece of paint splatter pine. Suction also stayed right up the whole time. After using it on the sanders, I sucked up some chips and dust from under the table saw. All the dust/chips/crap went in the drum. Opened up the Vac and check the bag - empty. Well probably a tiny bit of fine dust in it but I could not see anything.
Hooked up to Belt Sander
Now, before you email me saying 'why is there chips/dust under the table saw when you have your big cyclone?'. I did not run the big cyclone on purpose so I would have something to suck up with the little one. However, the dust port on the table saw does need attention as the standard one is a little one which I will be fixing real soon..
I had better point out something about the mini-cyclone (and big ones). To run the cyclone effect inside the drum and cone, some air power is required so there is a bit of a drop of in suction power compared to just using the hose straight from the Vac. This is not a lot and nothing in comparison to the loss when the Vac Bag get full or the filter getting clogged.
If you need a reason to make a Mini-Cyclone consider this - sanding goes much quicker,
results are better and you will get a bit more life out of the sandpaper disks/belts/etc
if you remove the dust WHILE sanding which means Time and $$$$ saved.
So, make one - they work great.