Just had a go at putting something like this together, not particularly successfully, I have to admit.
I was using what I had which was four of the straps that come with Alpkit dry bags, which have a quick release buckle at the end and conveniently come with a 3 bar slide. The advantage is that you can remove the bag and the harness more quickly (in theory), but the disadvantage is that you can only thread one end (male buckle end, with the buckle removed) through other components, so it took me a few goes of threading everything together, then taking it all apart again so I could put the right bit on first
The problems I had were that the middle 3 bar slide that holds the bar/fork loop to the bag loop, is able to slide up and down and so doesn't stop the bag from bouncing up and down. In Ray's photo, it looks like that slide is held nice and tight to the bag, but I've found I have a bit more movement and it slides up and down.
The other thing is that without the loop on the bars, or any other bar furniture to hook it round, the straps loop round the bar very close to the stem, which makes it less stable laterally. This could probably be solved with a couple of lock-on grip rings from some old grips (which I may have lying around anyway), but that means taking my (foam) grips and levers off so a bit of a pain.
I should say this is meant to be critical! I really like the idea and will spend some more time fiddling at some point, but for now I'm going back to my MYOG harness.