The MX6 doesn't look all that heavy but if you look at how the QH is attached, there's not a lot of stress on the QH frame itself. It's just basically setting the spacing of the links. The plates at the top-link/hook are taking most of the stress and they're mounted parallel to the tension load. The lower pins go through the lift arms.
I use an old Ford 954HD that probably weighs twice the MX6 and I've bounced it pretty good going a bit too fast up my pot-holed dirt driveway. I have the HF model and it's held up well. No breaks or bends yet.
Forgot to mention: If the QH frame were to bend, It would most likely be the top (horizontal) bar but I'm betting you'd break the top link pin first.