Mr Squid will undoubtedly explain this far more elequently than I.
As far as I know, there are two reasons why you oil your chain - firstly to stop the outer surfaces getting rusty; and secondly to lubricate the contact with the sprockets.
On the second of these points, this really doesn't take much oil, and I don't see how the dual injector really helps this. Perhaps if you're riding in exceptionally filthy conditions and need the extra flow of oil to wash the chain?
If anything, by fitting this, you'll just use more oil, as well as incur the expense of buying it in the first place?
