To clarify this explanation (sorry to resurrect an old thread but I fought with that recently and thought it could be useful) this only works if you set “time signatures” in the global settings to “polyrhythm”. “Polymeter” would affect the way the notes already in the track are played, which isn’t what we want here.
So you want to start with a 4/4 track, input notes (that will be on a quaternary rhythm), then switch the track to 3:4, then input new notes (that will be on a ternary rhythm), then possibly switch back to 4/4 if you want to input more quaternary notes (but the signature won’t change the way it plays anyway).
It’s indeed pretty fast to do once you get the gist of it, but not as intuitive as a triplets grid in daws. Although it’s more versatile, as you can have triplet, quintuplets (5:4), sextuplets (7:4) etc grids as you want.
Beware! 3:4 is different from 3/4!! that’s why “polyrhythm” needs to be set in the settings.
To recap:
BOTH X/Y and X:Y mean that a note of length 1 corresponds to 1/Xth of the bar, BUT they differ in how they set the amount of beats per bar:
X/Y means you’ll have (X/Y)*4 beats per bar, and
X:Y means you’ll have Y beats per bar.
(if someone can just confirm I didn’t get that wrong, that’d be great 
because I only recently figured that all out)
And that’s why the result changes when you set time signatures to polymeter but not when you set it to polyrhythms [1]: with a 3:4 you still have Y=4 beats per bar. That’s not the case with a 3/4 where you have 3/4*4=3 beats per bar). I guess that’s why “polyrhythm” is the default setting on the Pyramid
So yeah, I guess having just two numbers: number of beats per bar AND default note length would make things more intuitive and cover all use cases of both polymeters and polyrhythms, but, you know, music theory…
[1] BTW I believe the correct way to put it in the settings should not be “time signature = polymeters OR polyrhythms”. It should be “track signature = time OR rhythm”.
3/4 is a time signature, 3:4 is a rhythm signature. None of them is inherently “polymetric” or “polyrhythmic”, as you need in both cases at least two tracks (or two melodies/bass/drum lines on the same track) to get a polysomething.
And technically a track should have BOTH a time signature and a rhythm signature, but when you set a rhythm signature the Pyramid forces a 4/4 time signature (I think).