Well, any .22LR can accept a PVC based suppressor perfectly fine. Aluminum is more "trick" and like the "big boys" but considering the "expansion ratio" between the tiny .22 bore at rimfire pressure to the relatively enormous volume of almost any suppressor design (especially the home-brew variety), total "flat plate" pressure is quite low.
As you posted, the GSG faux suppressor does provide an important and needed function...it stabilizes and centers the relatively thin, "whippy" barrel. in fact - and I have not tried this, if one were to shoot for accuracy without the faux suppressor installed I would expect a noticable degradation of accuracy because the barrel is completely UNsupported from the receiver forward.
You will note that when installing an aftermarket barrel extension/muzzle attachment, the "spec" calls for the barrel to be trimmed and angled so the attachment acts to "center" it.
What I did with the 16" carbine barrel was to fabricate a 16mm x 1 mm "zero tolerance" bushing that when screwed down snug in the front sight base, aligns the barrel with ZERO axial play. By leaving the threaded section "long" any style "faux" suppressor could be created.
I realize it's not "pc" these days to discuss how to build a suppressor, but the fact is, ANY device that attaches to the muzzle that lowers the sound-report is considered by the BATF to be a suppressor. Even a completely open tube, if it resulted in a lower decibel rating would constitute a suppressor by definition.
I've played with "pop bottle" suppressors in the (distant) past and found them to be FAR more hype than practical reality. In fact, depending on variables, adding a 2 liter bottle to the muzzle can actually INCREASE low frequency sound generated by the .22LR due to the "drum effect" of the large volume container, and low frequency sounds travel farther than high frequency. So the "ear" hearing the sound may not intuitively know it is hearing a gun shot, but it WILL hear "abnormal sound" and take notice.