Hmm, hard to say exactly, but I have the 4" version on my Rockler 1250. I've emptied the drum more than a dozen times in 3 years but the filter bag has a light dusting around the perimeter and maybe 1/2" thick gathering at the bottom. The filter is the same, just a light coating of dust. I'd estimate the cyclone gets in the high 90s of dust. I would think the clear "Dust Deputy 2.5 Deluxe All-Clear Cyclone Separator Kit" that they have is quite similar in performance.
A bit off topic, but I also have the Festool cyclone and in the 3 years I've owned that the bag/filter are in similar condition...basically brand new and little to no dust. It is, as a unit, more low-profile and still very effective (not counting the extractor of course). I will say you lose a bit more suction but 90% of the time I use the 36mm hose and it's barely noticeable. For sanding/domino/router work the 26mm hose and suction is still extremely good.