I think Doctor Gollum is seeking problems where there is not any.
- Bush is perfectly supported for any forces that are directed to it. It is one mold piece and needed to be forced through arm and is very tight fit to arm. Will not pop off, because of tight fit to arm and also flanges of attaching points are holding polybush in place.
- On emergency braking or cornering, there is more bushing material (cross section area) taking the force than on original rubber bush. I can not think any force directed to arm that original rubber bushing could handle but this polybush could not. It is more likely that rubber bush would tear up before this polybush.
- Movement of arm is ensured, because material is soft enough and bushing is shaped to allow movement. This is the thing that will break the arm if movement is prevented because of too hard material and/or shape of bushing. Nothing else, if arm is as good quality as it should.
- Bushing is molded to one piece PUR so it will not tear apart in any circumstances and also polybushes are proven to be more durable than rubber bushes. More likely arm will destroy original rubber bushing than poly bushing.
- I've seen old rear rubber bushing, teared little bit as it normally does when it ages. That is much more security risk that this polybushing. And people are driving with bad condition rubber bushes many thousands of kilometers still with no arms to tear apart themselves or bushing.
I've been driven with this current setting about 25000 km. Last MOT was two months ago with no notes and week ago I was under the car checking for idler arm condition and checked arms (in place) but it was possible to see that both arms were OK (no cracks or bends).
I do like to drive corners fast (because current settings allow this with no trouble) and also I often need to drive un-coated roads (gravel roads) with big potholes so I could say arms are driven in very harsh conditions and i believe something would been shoving by now if there's any problems with that rear polybushings.