I think issue is the shape of the indentation where the cover goes, which differs between the two cases. The Graugear heatsink and the vented covers I linked all seem to have compatibility issues with the Slim revision, but you're right that the Sabrent heatsink apparently doesn't.
Thanks for replying! I'll update my comment.
P.S. it's kind of amazing how Sony requires SSDs to have a heat sink, but then built a compartment for them which has almost zero airflow. I wonder how many people who upgraded their SSDs are simply running without the metal cover, although I expect this might have the potential to cause EMI problems.