Use them on Tiguan on winter wheels for 10 years. Never had an issue. Found really nice 16" wheels for cheap, brand new, but needed rings. And, that is about it.
For $20 I'll get the metal ones. Matching wheels to hubs isn't always possible especially in aftermarket. And, like you posted twice, they ensure the wheel is centered on the hub. Guys working at tire shops are aggressive with impact wrenches, so the wheels are not on straight half of the time causing an out of balance condition.You can get metal ones, but you need to either make sure they’re anodized or put a tiny amount of antiseize on them. The biggest problem with plastic ones is guys who track, they just melt.
Good wheels will typically come with metal ones.