I've always been told that the purpose of lubing your chain is to keep the o-rings lubricated and to lube the contact with the sprocket. (Not the same thing).
With the normal Scott Oiler only the outer O-rings were getting lubed. I had the same problem on my Triumph Trophy. In fact it hardly worked it's way onto the chain rollers either.
Fitting the dual injector won't use more oil AFAIK as the drip rate is set at the reservoir. If you have two outlets at the chain end I think you're getting half a drip at each. It just spreads the delivery of the lube.
I'm prepared to be proved wrong though!
P.