One of the big story lines last year (at least in the financial advice business) was the headway made by so-called robo-advisors, that growing breed of low-cost, online start-ups providing financial advice and investment tools aimed mainly at mass-affluent investors.

According to Corporate Insight, the total assets managed by 11 leading robo-advisors reached $19 billion as of early December and were up 65% since April 2014. That’s still just a drop in the multi-trillion-dollar bucket of professionally advised assets, but it’s not an insignificant sum, either.

“The amount is impressive considering how young these firms are and that most of them have been around only for a year or two,” says Grant Easterbrook, an analyst at Corporate Insight, a New York City-based research company that covers the space.

The 11 companies in the headline number range from Wealthfront and Financial Guard, which provide automated buy-and-sell advice, to Personal Capital and Rebalance RIA, which enable users to work one-on-one with a human as part of their paid service.

“There are a million ways to slice and dice who the leading firms are,” Easterbrook says. “Some robo-advisors say they’re the largest by growth, or total AUM, or by revenue, or by free or paid advice. Betterment and Wealthfront are the best-known in terms of the PR they’ve gotten, but there are different ways to define success in this arena.”

By whatever measure used, the success of the current crop of robo-advisors is inspiring both start-ups and traditional financial service powerhouses to enter the fray. In the latter camp, Charles Schwab, Fidelity and TD Ameritrade all announced plans last year to add some degree of robo-capabilities to their systems.

Newer small firms, however, might be late to the party. “Just because Charles Schwab and Fidelity are entering the space doesn’t mean it’s the end of the world for these start-ups, because the pie of investment dollars is pretty large,” Easterbrook says. “But there are a lot of firms in this space and there’s getting to be some redundancy, and not all will survive long term. That’s typical of the start-up world. It’s not easy to build a new consumer-facing brand, and they have to raise a lot of venture capital money to do it.”

And then there’s the term “robo-advisor” itself, which has reached the point of overuse. “It’s applied liberally to anything that’s a new online solution mainly related to investing or personal finance, and the term per se is getting confused,” Easterbrook says. “To me, the key commonality among robo-advisors is they’re online-focused; tend to have lower [investment] minimums and costs; are about maximizing investor returns through low-cost passive funds; have no conflicts of interest; and have better websites and mobile apps.”

He believes robo-advisors have already made an impact on the financial advisory profession. For starters, they’ve helped drive down costs and create greater transparency on prices, and they have prompted traditional advisors to boost their website and mobile platform capabilities. And, of course, they’ve motivated several large retail investment firms to create their own automated investment advice solutions.

In other words, expect robo-advisors to remain a big story line in 2015.