That looks like a set of eccentric Rear Trailing Arm Bushings (RTABs). Those are commonly used, but on these cars do not provide enough camber or toe adjustment to be of much benefit. The weld-in kits offer far more adjustment, which is certainly needed for a car that has been lowered even by an inch, which almost all aftermarket springs do.
Another note: those look like they're made from polyurethane. Polyurethane RTABs squeek. OEM Rubber RTABs do not.
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