Derek Cohen (in Perth, Australia)
Barry, all cyclones - anything between the source of dust and the main sucker-of-dust - will reduce suction. It is all a compromise, however.
I have a friend who is a true expert on air cleaning, and he constantly makes this point, and advises that this creates a less efficient system. However, when I removed my Super Dust Deputy (the large version of the Dust Deputy before the duct collector), I found dust on the equipment. Returning to the SDD, matters improved. The cyclone was filtering the dust and giving the DC less work to do.
The same applies to the smaller cyclones. Consequently, you lose a little suction, but you gain efficiency in cleaning at the filter.
I use a Dust Commander on my Festool CT26e as it is antistatic (and the dust deputy is not).
The steel paint tin is also better at resisting collapsing, which plastic bins may do.
Regards from Perth