Monomachine only has a single stereo in for FX processing though, whereas the OT has two.
However the MM has 3x stereo outs, whereas the OT only has 2.
The OT has 8 tracks x2 effects, whereas the MM has 5x1 (Input track + 5 effect tracks) (+delay+distortion+eq+filter per track though)
OT has a much larger range of effects to choose from. Plus the live sampling can offer more on top of that if you are inventive enough.
OT also has the slider and scenes for more effects performance.
Both MM and OT have 3 LFOs but the OT has the ability to create custom LFO shapes.
OT also has more options regarding it’s sequencer, one shot/detached tracks plus different time signatures and step length per track. (which are amazing for effects, as you can create evolving patterns)
The MM has 3 send busses though, so you can have parallel effects processing, whereas the OT is always linear via neighbours and master.
I’d say sound quality wise, they are about the same, neither is amazing in the way a strymon is, or even as lush as the effects on my virus ti, but they all have their sweet spots.
No effects processing on the RYTM btw. You can send it through it’s compressor, and that’s it, i believe.
I don’t have an A4, so i can’t comment, but i hear the reverb is pretty lush. It’s shared across the device though.