In addition, the report found, hybrid robo-advisors — such firms as Vanguard, Personal Capital, Rebalance IRA and AssetBuilder, the report said, which use technology to standardize and cut costs on the information-gathering side of the job but have humans to "seal the deal" — do better, at least in the United States, because those human advisors are proving to be more effective in getting clients to commit.

Robo-advisor growth in the United States has been swift, with assets under management rising from $11.5 billion in April 2014 to an estimated $61 billion in June 2016.

Pure robo-advisors have seen their growth slow as the market matures, the report said, with Betterment's growth rate for assets under management at the same place it was a year ago, and at Wealthfront AUM growth, according to Forms ADV, "down to barely $60 months per month over the past six months."

That's due, the report said, to clients "starting to realize that what they're getting from many providers is little more than a passive portfolio that they can easily build on their own without the robo middleman."

Benefits such as tax-loss harvesting and the automation of the rebalancing/reinvestment aside, that slowing growth is leading to a rise in hybrids.

But on the pure robo-advisor side, firms are turning to aggregation, with Betterment and Wealthfront both adding it in 2016. Still, robo-advisors have as yet only managed to capture 0.2 percent of the of the "overall $37 trillion U.S. savings market."

But robo advisors will capture a "more meaningful share," the report said, as additional factors come into play: the entry of more non-robo firms into the robo-advisor segment; increasing awareness on the part of consumers; and the harnessing of existing RIA, certified financial planner, and broker channels by robo-advisory services to accelerate their customer access and bring down customer acquisition costs.