The most minimal drive mounting system I could think of! It leaves enough room between drives for airflow and cable management and is extensible. I only have two drives at hand, do upload a make if you used it for more.

The stackable (multi) variant, well... stacks. You can clip these on one another. There's a very simple locking mechanism and the tips of the clips are slanted - these make for a snug fit and a stack that doesn't slide apart.

The single variant can be used for single drives, but it also clips onto the stackable variants, so it can be used as an end piece on the top of a stack.

The clips double as feet for when you're working with your drives on a desk.

Printing, materials, strength

I used PETG with 25% infill, haven't tested with anything else. I haven't load tested this, but 2.5" are very light, and based on experiences with the same clip design, I'd easily go up to stacking 4 drives if using PETG.