Suspension Component Breakdown

[goldvn05]

hi guys,
Am considering installing the Rear subframe insets bushes.
https://www.nolathane.com.au/product_detail.php?part_number=49169

any issue people have had installing these? (with subframe still on car)

from this bellow pict, this is not mine, pict found online,
What is the rubber thing at top of subframe mount(red arrow)? on mine its loose and can rotate it a little.
do you keep it ? and does it cause issues with the subframe insert mounts?

thanks