Some thoughts:
Extraction will likely be less than what a DD can archive, especially on the fine dust fraction, as of the geometry:
The cone of a cyclone is ment to accelerate the particles so that they'll have enough momentum to continue on downward and separate from the airstream at its turning point. The festool thing looks like a dustcan type extractor, while these are somewhat OK for bigger particles these usually fail at the smaller/fine fraction. Might be OK to use with the CT in AC mode and a Planex (as depicted), or to collect chips from a router (unless these tend to clog inside the inlet as it has a narrowing section) - but I suspect a DD will overall perform better (especially when sanding with higher grits).
The bins being transparent is good so you can watch the fill grade, question though is if the bag won't simply turn opaque and leaving you non the wiser. I dislike how the bins are stacking though, they're not deep enough to fit the lids, so you can't put a lid on the top one leading to you being unable to stack something ontop as there isn't an even surface (or you'll have to also stack the lids, opposed to how it's depicted). The rim (and handles) could have been created different (smaller, with the latch of the top systainer going into the handle instead of an extra slot) to give a better stacking ratio than 5:2 (excluding the lids that protrude over the topmost bin) that can be deducted from the bin carrying picture.
The bottom adaptor dosn't seem to be able to lock onto the bins, thus there dosn't seem to be a single-hand way (as the handle on the top systainer most likely can't be used) to lift the CT over an obstacle. But it looks like it'll have enough space though to store the additional hose for transport. Possibly it can be used without a bin (just a liner bag in the bottom part) for ~1/3 of the capacity of a bin, but that will have the downside of no visibility at all.
EDIT:
It dosn't look like it's worth spending (all prices as of the german homepage incl. VAT) 416,50€ on it - or 184,45€ on a 3 pack of bins (that's 61,48€/ piece) or 83,30€ in case you buy one in a single pack (that's 3€ less than a SYS-5). Comparing the pricing for the bins to the 41,65 € they call for the part (a socket with short extension and plug) that moves the outlet to the top part of the pre-extractor (which seems to be a must-have in case you want to use a sleeved hose) makes that part look cheap in comparison.
Given that similar sized transparent containers (20L) can be at obtained at IKEA for less than 5€ (which would make them 10€ when molded in thicker to have higher stability) I can only assert that such ripoff pricing dosn't make me want to continue buying their products...
