I'm running the same set up with my SF2, shrimp and 20" coops. I haven't noticed any honking from being on OC, but maybe I've just been noticing how loud the bubbles are rather than listening to the reg. I also plan to use it as an intermediate step- switch to OC on the BOV at first, assess the situation, then if completely bailing off the loop swap out to a dedicated OC second stage. My only issue with the set up is figuring out a good way to route the LP hose from the bailout to the BOV. Tried a few different options, but haven't found one I like yet.
I did use the BOV in anger once. It was my second or third dive on the backmounted unit so I wasn't familiar with some of the nuances. I was coming up from the 15' stop, reached the surface and the hud started going crazy with three different readings. Since I had to concentrate on not getting taken out by the boat and ladder I just switched to OC and climbed out. Turns out when you go vertical the condensation in the head can drip right onto one of the cells. I haven't had it happen since, but I try to knock on the head before going vertical when I think about it.
-Chris