So, my Offroam mount came today, and took all of 60 seconds to install. The machining, design, concept, and packaging are all excellent. It's super-stout and doesn't move at all, is padded in all the right places, and is dead simple to operate. I've been waiting a long time for a clamp like this. No drilling (I was starting to resign myself to that as the best/most sturdy option), and can easily be placed to not block the vents and stereo. Unless it fails catastrophically or becomes unable to hold firm over bumpy roads (neither seems likely), my search is over. Will certainly followup if either of those come to pass. Great job, Offroam!
Oh, I would also be remiss if I didn't point out that Offroam was great to deal with. I received a proactive note from Alexa thanking me for the order, and double-checking to see that I'd seen the note on their website that the order would ship this week (not last week). I hadn't, so it was awesome of her to reach out - I suspect by the weekend I'd be wondering why it hadn't shipped yet. :-p