Do you have problems becoming disoriented when you are in complete darkness? If so, the #13 filter can help.
“Photography is a complex and fluid medium, and its many factors are not applied in simple sequence. Rather, the process may be likened to the art of the juggler in keeping many balls in the air at one time!”
Ansel Adams, from the introduction to The Negative - The New Ansel Adams Photography Series / Book 2
I have used one while printing solely for the purpose of helping to put large sheets of paper into processing tubes. It is still very dim, but I had less kinks in the paper that way. Your time under a safelight with RA-4 is very limited before fog is induced, so be careful.
The only one worth it (that's easy to find) is a Thomas Duplex. I don't know if the filters are even available any more but I printed with them on in a community darkroom a few times and it was amazingly bright (still much darker than b&w) and caused no fogging.
I have one that I use when printing RA-4. I have a roller processor, and find loading exposed prints in in the dark is fine, but sometimes things have been set down on the lid, and they go flying when I open the lid in the dark.
Mostly it helps figuring out where you are turned in the room. It was more useful before I had fitted the Omega D5 in as my primary enlarger. It has illuminated dials for flitration that help me not bash my head against the enlarger head, as I was wont to do with the prior enlarger without use of the #13 safelight.
Mine is an indirectly aimed little safelight - glass of the size of the Kodak duplex safelght. 7.5W bulb.
You need to be in the dark for quite a while before your eyes begin to sense that this thing is even spilling any illumination out at all unless you are looking directly at it.