Since I change the hard drives for each project, I have not screwed on the handles. Works wonderfully. But it is important to shut down the units before changing the hard disks.

I did not unscrew the handles at the beginning. As it turned out during operation, the handles are useful for the airflow but also for stabilising the HDD. The HDDs do not fall out, but there can be noises during operation because they are not seated properly. Since I fitted the handles, everything is fine.