Not quiet in my opinion, very loud bark unsilenced
I have a mk1, no threaded barrel. I sourced a new barrel (for a zoraki hp-01) from a french website, brought a half inch adapter (solway) and a silencer from Air-Fective Tuning, not the biggest but doesn't look stupid.
I think they are noisy without a silencer, no pronounced "bark".
I can hardly hit anything at 10M, eyesight and age not on my side.
Solware - Webley Alecto MK3 ½ UNF Silencer Adaptor
www.arprotech.com for barrel