Sure, it holds the MRCC into a 19'' rack well enough, just as expected.
The few connectors and buttons on the MRCC's side remain accessible from the front (or back). Not as conveniently as in desktop position, but still easily enough.
Just one thing: you'll need to unscrew the MRCC's side screws in order to install these ears, and those are hex head screws. There's no included allen key, so make sure you have the right tool for the job.