I believe the Rosewill RSV-L4500U and its variants are fairly popular DIY server rack case because of their (somewhat) cheap price. I'm in the middle of swapping out the 3, internally-facing drive cages on my L4500U with 3 Rosewill RSV-SATA-Cage-34 hot swap cages and discovered several "gotchas" with the process not documented elsewhere. I'm dumping all of this here in hopes it helps existing owners and future buying decisions.

Molex Power

Power is delivered through molex connectors, NOT sata. There are 2x molex ports per cage that power all 4 drives (and the fan). Sata-to-molex adapters can be huge fire hazards when not using crimped sata connectors so make sure you have a source for quality male sata to female molex adapters (I could not find any on amazon...) OR make sure your PSU has enough perif/molex cables.

Fan Connections

The fan connections on the cage do not support PWM fans. They are 3-pin connections. This isn't a huge problem though as the fans are easily removable and are positioned on the back of the cage so if you use PWM fans they can be accessed easily to be powered however you want.

Cage Orientation

The product page for these cages shows the cage (and trays) oriented in a horizontal position as well as stamped "TOP" "BOTTOM" text on the cage sides. However, to fit properly in the existing cage slots on the L4500U the cages must be oriented 90 degrees so the trays are oriented vertically.

This is not a bad thing...drives should be able to operate in any orientation and the vertical orientation does not detract from the functionality of the cage so this is more of an FYI If you care about the aesthetics of the horizontal orientation.

Cage Fit (In)compatibility

As-is these cages DO NOT fit in the cage slots of the L4500U. The external dimensions of the cage are identical to the existing L4500U internal cages BUT the front face plate of the hot swap cage is like ~2mm too deep -- it bumps up against a raised metal lip in the chassis that is just inside the front of the case. It's not clear if this is an intentional design decision on the actual hot swap chassis (L4412U) that enables these to fit (make these cages just replacements for that one chassis) -- or if this is a design mistake on the cages that are supposed to fit the L4500U but was overlooked. It's really, really, close to fitting. However...

The cage can be non-destructively fixed to fit the cage slot. The front face can be detached by unscrewing two phillips head screws. By then angling the face plate slightly -- with the bottom of the plate staying flush and the top of the plate protruding 1-2mm -- the cage will slide into the chassis correctly and the chassis front door can still be closed without mashing the face plate (see pictures). This does not affect the functionality of the cage at all, as far as I can tell. Trays still slide in/out fine and the face plate led ribbon cable has plenty of slack. So these cages can still be used if you are ok with it being slightly unclean looking.

The face plate itself is also pretty deep with the PCB for the led board being shallow compared to the depth of the entire plate. I suspect one could easily sand or cut down the lip so the plate would fit flush.

Other Cage Notes

The metal strips located on top the top of the existing, internal cages that are used to "lock" the cage in place can be re-used for the hot swap cages.

If the the cage is oriented vertically with latches facing up then the power/data connections are also facing upwards which is super convenient for access and cable management.