I am very happy to report that the tubeless-ready Flintridges on non-tubeless rims haven't blown off while I'm biking 30mph down the Alberta Street or Post Street hills. I took it pretty easy the first week or so, even turning into corners gingerly. After a few rides I started having more confidence in them and now don't worry too much.
When inflated under 40 psi, they can feel a little squiggly on the street so I keep them in the lower range of 40-50 for street riding. The sidewalls state inflate between 30 - 50 psi.
Here's a closeup:
They're a lot knobbier than they need to be, and at first the rolling resistance seemed higher than the Clement X'plor MSO's. They roll better now on pavement, maybe because I've worn them down a bit and found the sweet spot for psi. On dirt and gravel they are great, and a blast to ride.
I'm still curious what'll happen if, I mean when they get punctured by a nail, staple or glass, so I've been heading straight at glass on the road and riding through construction sites. No punctures yet, but I keep a couple CO2 cartridges and tube in my pack in case the tire deflates all the way and doesn't stay seated.