The best Catch Cans; are a simple well constructed catch can, without any internal medium and an efficient separator.
Mediums are not required and don't distinguish them as a more efficient CC. Mediums can often cause internal engine breathing problems, ie, small filters, micron metal filters and steel wool, (i'll explain further below). Well manufactured cans permit a free flowing of vapor material and fluid into the bottom of the can. They settle quickly to the bottom of the can and are not picked up and recirculated from air flow.
Internal mediums trap & hold material and water/oil vapor, which aren't allowed to quickly settle to the bottom of the can. These vapros and material remain higher in the can, recirculated from the medium.
Carbon deposits are formed from water and oil vapor exposed to constant high high temps. They're literally baked on internal parts, it washes over. The more oil/water vapor that's trapped in the bottom of the CC quickly, the less issues with carbon buildup.
Another point to keep in mind is; Mediums will also freeze with water vapor from the crankcase, causing a air flow problem. If this occurs, such produces higher internal pressures and these higher pressure can cause blown seals, oil circulation/starvation issues, etc. This is why the CC needs to always be positioned near a stronger heat source so it will heat up quickly and allow both air and vapor to circulate.
Catch Cans also require maintenance; draining, flushing and cleaning to remain efficient. This process also includes the line a longer intervals than oil changes. Intervals need to coincide with oil changes. With a medium in the CC, it makes the 3 points listed above more difficult. The medium must also be removed and the same process applied then reinstalled.