I have no idea why ZDZ would do that. If they have concerns about felt fibres entering the carb screen, a small instruction can cure that risk.
If a felt clunk is washed/massaged in gas well before fitting, all loose fibres will be washed out and the filter is ready to go.
It has a few advantages in that it will eliminate suction line bubbles, regardless of fuel foaming in the tank. This clunk type also will draw fuel from the tank until it is bone dry, and it filters absolutely everything out!