There's nothing particularly different in this approach as plenty of other providers take the multi-manager route. A BNZ executive quoted in another publication (whose name escapes me) did point out that the Russell relationship is unique in KiwiSaver, for an Australian-owned bank at least, because it doesn't own the underlying investment business as well.
This could remove some potential conflict-of-interest for BNZ, plus it's also easier (and cheaper) to fire a third-party fund manager if things don't work out rather than disestablishing an internal crew. (However, Russell, which already manages some KiwiSaver money via the Aon scheme, has to date performed pretty well in the league tables.)
And even though BNZ has delegated certain duties to Russell the bank, as you would expect, maintains strong controls over the manager. The 'Statement of investment policy and objectives' lays out the varies responsibilities of each party to an almost anal level of detail.
BNZ, for example, retains the right to penetration testing and ethical hacking to ensure Russell systems are up to scratch.
As reported elsewhere, too, BNZ will be counting on 'organic' KiwiSaver growth (ie mainly by 'engaging' with existing customers) rather than acquisition after bowing out of the battle for Tower.
It is understood ASB, a consortium of TSB and Fisher Funds (backed, allegedly, by private investor and Infratil board member, Duncan Saville) and a mysterious 'Australian boutique fund manager' are still chasing Tower's investment business.