This confuses me a little since the vast majority of the funds they invest in are Vanguard ETFs. Maybe you mean >something more specific that I'm missing?

Haha, ok. So you can just go buy a Vanguard target-date retirement fund and let the fund's internal structure take care of the asset allocation for you, or you can go talk to somebody at Vanguard who will either give you some straightforward advice about how to build your own portfolio for a one-time fee or build your portfolio for you for an ongoing fee, or go to Betterment where they will build you a portfolio out of Vanguard funds, or you can build it yourself using some of the insights you gleaned from this article. All of these are reasonable solutions.