The subsonic thing mostly affects the sound down range. Behind the
barrel you don't hear much of the crack but you get all of the gun
noise. 22rf drops below super sonic pretty fast anyway, particularly
out of a hand gun.
I have a couple bricks and they seem very quiet in an unsupressed
rifle. They make up for the low speed with more weight to maintain
down range performance.
Why not use .22 shorts?
I think that 65gr bullet would do better on squirrels if that is what
you do.