grub screw silencer

I want to install a silencer/adaptor/compensator on my air soft with barrel width 11 mm for asthetic sake.

There is no thread on the barrel head so I could only use silencer/compensastor with grub screw installation.I find some silencer on ebay, but they are for air guns which are over 2 J. I don't want no trouble and I just want to know where I could buy higher quality silencer that fit the barrel size of my airsoft in Hong Kong.
Are those silencers available at Kwong Wah Street really help dampen noise?

I expect to spend HKD500-2000 on the item. Please kindly suggest.
Thank you very much~!