Some fintech startups are innovating so quickly that it's hard for outside counsel to keep up.

Ben Alden, general counsel for personal finance startup Betterment in New York, has hired many firms that he ultimately parted ways with before finding the right outside counsel who understood the company, which offers automated investing, or “robo-advising.”

“It's hard to get someone who's billing $1,000 an hour up to speed in a cost-effective way,” Alden says. “We would spend a lot of time [and money] to train outside counsel on our specific industry.”