To me, this is Apples and Oranges...
I don't have an eq6-r, but I did look at them when I was making my purchase decision, as they are often recommended here. I required portability, and the eq6-r was itself heavier than I wanted to lug about, and its payload capacity was far larger than anything I wanted to hoist up on it. So there's that. For a quality comparison to be relevant, you'd need to determine whether the eq6-r would even make it to your short list on that basis (or, for that matter, budget).
The iOptrons were closer in portability for me, and I looked at them as well.
I ended up with an EXOS2 PMC8. If you try to judge the mount by its unguided performance, you'll end up pretty much validating what's said above about mechanics and price. Mechanically, it's an LXD75 with ball bearings on both axes and the worms. Lots of people seem to have liked the LXD75's back in the day, but it is what it is.
But this mount guides well. What's different is the power train and the controller. Where does periodic error come from? Rotating components. What's rotating? Not much - a small pulley on the motor, a large pulley on the worm shaft, and of course, the axis itself. That's it. Not even an idler on the belt. Take care with your mechanical adjustments and PECprep will show you a fairly smooth periodic error that's pretty easy to guide around. And you don't have to guess about those adjustments - after I figured out what was needed, I wrote up a short tuning doc and published it on the PMC8 support forum.
Then there's the PMC8 controller - part of what sold me. I quizzed Jerry a lot on that, pre-purchase. I'm a retired IT architect, and because it was so different, I wanted to understand. When I finally understood his design, and for that matter, the chip he based it on, my eyebrows went up. Only somebody with a real eye for reliability would have made the choices he did.
And the PMC8 is control-program agnostic. ASCOM, INDI, ES's own (Visual) 'Explorestars', and if something else comes along later, just write a driver that speaks the PMC8's well-documented control language, and you're good to go. People control them with all sorts of programs, so no, it's not a toaster and you do have to think through what you want, but if you value flexibility, it's there.
I'm careful with my guide ratio, balance, and adjustments and I typically am able to guide 180s, 300s, or 600s exposures, at 621mm or w/reducer, depending on target and conditions, with round stars. Talk about price vs quality all you like - if you are prepared to give this mount what it needs - and I think you do need to do that - it can punch well above its price point.