Indeed, my rear one got 5 sizeable dints on its first ride but only on one side of the rim (got one on the other side on the second run).
However, I emailed the guy at JRA (Jon I think) and he’d been testing them for a while and only damaged them on a rocky DH race so I think my rear one was maybe a dud. JRA have kindly offered to replace with an arch ex so I’m happy.
My front wheel has been fine though, even on some pretty rocky trails that I rode after swapping in my 819 wheel (bloody heavy) on the rear.
I’m not the type that notices stiffness/flex so can’t comment there.
Oh and they seal up pretty easily tubeless. (I use a 2.35 xr4 on the front and a 2.25 Rocket Ron (new pacestar type) on the rear)