Well, finally tried out the SPG clipped off to the left shoulder D-ring this weekend. Far easier to read with just a glance, no contortions/clipping/unclipping required, but I did grab it several times by accident when I was looking for the corrugated hose to dump some gas during an ascent. Not sure if this was just unfamiliarity and would ease with practice, or a persistent problem. I'm thinking of trying the "route it along the corrugated hose, held to it with rubber bands" approach for comparison, as that would eliminate having two separate hoses (and a bolt snap) in the same area.
For the open water diving I normally do it does seem to be superior, subject to eliminating the momentary confusion when grabbing the wrong hose. Having the two separate hoses didn't feel like it would be a safety issue, just a bit of mental "oh, that's not the one I was looking for" before I grabbed the correct hose. Still took far less time than having to unclip from my hip, and put all my dive info (wrist slate on left forearm, compass on left wrist, watch on right wrist, computer on right forearm) out in front of me, with a good scan pattern.
Guy