Why not both?
VR3, Shearwater and HS Explorer (I think) can be unplugged and used for OC.... if you must...
I thought part of the "fun" was sitting on the boat while everyone else dives trying to rewire your rebreather with a Rusty Leatherman tool and a Soldering Iron with a tip like a snow plough
Seriously... I just use a Timer and Tables on those very rare occasions or if the Surface Interval is long enough drag the Vyper out of tool box and use that.
BEN