Hi
I have the plenum insert and the Parker Hale for mine. I've not tried the AA silencer so I can't comment on that.
The plenum insert does quieten the muzzle crack down quite a lot, but isn't as effective as the Parker Hale. The PH is a screw straight in job like the AA but is cheaper at £14.95 with free delivery from Ramsbottoms. It quietens the rather loud crack right down. Some people say that a silencer is a waste of tme on a springer as most of the noise is from the spring itself. Perhaps my HC is quieter than most as most of the noise from mine is muzzle crack and the spring is quite quiet.
Saying that, I use the plenum insert when out and about as it doesn't add any length to the gun, which makes it much handier to lug about! It quietens the gun down enough for most outdoor uses. Funnily enough, with the insert, there's a sort of "boinnnng" sound from the gun! Not there with the Parker Hale. Odd...
Gareth