Ok here's my feedback.

Thanks to that last comment Lax, i believe it does now work as intended, and I'm not getting any jittery mouse action.

basically i had the concept of the repeater regions wrong, i thought you created a region that was automatically replicated on all machines (and that seemed the case as i always 'sync'ed my RR) whereas in fact it's just a region to replicate whatever comes from that wow instance.
In short, RR are not global for all wows as i thought, but instead are specific to a wow window and passed to a specific set of other wow windows.
Not sure i'm writing this clearly, but the concept is clear in my head i think

So now i have couple questions to make best use of them.
I have my main on one machine (say Machine A:1) and 4 slaves on the other machine (lets say MachineB:1, MachineB:2, MachineB:3 and MachineB:4)
My healer is on Machine B:4.

so on MachineA:1 i've created a RR on top of my grid bars for my healer to click heal with clique.
Now when i create it, what target should I use? I only can select either 'all targets' or '1'?
for now i've used 'all target' as it doesn't matter if my dps click the grid as well (since they have FTL targetting) but wondering if that's the way to go.

Since i want to be able to lead from any toon (and heal the same way) i'ce also created RR from each of the other DPS toons (MachineB:1-3)
This was a no brainer as the target dropdown showed the number '4' (my healer) and i could just create that RR easily.

Now, is the fact taht all those regions are on top of each other a problem?
doesn't seem to affect the mouse, but wondering.

thanks again
-Zub