The reserver is 20-50% faster depending on what you're doing, has dual channel memory, can accept 64GB, has 2 m.2 slots, pcie expansion, external antenna connections for internal wifi, cell, or sdr cards, better build quality, a built in arduino coprocessor with i/o pins, and in my experience rock solid stability.
The r1 advantages are toolless drive caddies that you don't have to disassemble the chassis to swap drives, likely lower power consumption, and far cheaper, unless you can find the reserver on sale in which case the r1 is still less expensive.
I have two reservers, one is doing NVR duty running scrypted for four cameras. It runs at about 4% load recording 4 full bit rates streams and doing motion and object detection.
I don't have an r1, but do have another similarly specced n100 machine, that I could wedge a coral into. It ran at about 20% usage with the same load, but I'm pretty sure it could have been brought down some, as I was streaming onto a NAS connection, and hadn't properly gotten the igpu accelleration working.
Hope that helps a bit.