Everyone should work on a CMYK workspace, i'm even not sure that RGB printers still exists, those were produced long time ago at the time when printing at home was still expensive. Now, all printers are based on CMYK (they all have at least 4 ink cartridges, some have even 8 cartridges to better handle color profiling for photo printing).
RGB workspaces are only used now for web design and video systems.
The color management system of the printer should (i insist on should) handle correctly the color workspace conversion to the right profile used by the printer and you should (i insist again on should) get a clean print, similar (or almost) to what you have designed.
But the closer you design your project to that profile, the less artifacts and the less color change you will have. So the best is to work CMYK as the printers have their own CMYK workspaces, but the gap between those workspaces is less than RGB to CMYK as the colors are coded completely differently.
This is from my own experience when i was working as graphic designer.
When i was professionally designing posters or magazines, i was working on a calibrated screen that was providing a color profile for photoshop and illustrator, so i was sure that the color showing on the screen, was the color i have decided to choose, this is the best (perfect) approach. But really expensive.
In my design, i have a lot of gradients with alpha blending, the conversion from RGB workspace to CMYK is killing all the work.
This is the result of the conversion just for comparison

- YaYa---GB-Box-Template-CMYK.png (3.3 MiB) Viewed 33172 times
The result is ugly, and a lot of artifacts appeared, the blending are not blending anymore lol
Here is the original design (in RGB, exported in RGB with a RGB workspace) to compare side by side

- YaYa---GB-Box-Template.png (2.78 MiB) Viewed 33172 times
You think i'm nut and perfectionist lol but this is a similar approach as the pixel perfect themes for our 3.5" screens
we do not want a basic down-scaling from whatever to 320x200, no, we want it directly designed for our screens, in 320x200