"That's about one in four, underscoring the importance of a quality bank app to keep your churn low," Fletcher said.

Though lower fees, better customer service and relocation were bigger reasons to switch institutions, the fact that mobile-app quality beat out incentive offers, better interest rates and branch locations is still significant, he noted.

He noted to be careful trying to monetize mobile apps, however – 76% of respondents said they refuse to pay even $3 a month to use them. Financial institutions on the west coast, in the south, and up to the mid-Atlantic region may have the best chances at charging members – as many as 28.2% of respondents there said they'd pay. Age makes a difference, too: About one-third of people aged 26 to 35 said they're willing to pay $3 a month to keep using their mobile bank app, but that drops to just 25% for Gen Xers and to 23% for people under 25. Baby boomers and seniors were the least willing to pay, the study found.

"We think making money with a bank app is probably going to be more nuanced," Fletcher said.

Almost half of the respondents said their banks' mobile apps are not missing any features, but for those who wanted more, person-to-person payment capability and information about savings account rates topped the wish list, according to SNL. Checking account rates, mortgage rate comparisons and a click-to-call customer service feature also ranked high.

That wish list isn't something to ignore. Fifty-four percent of the respondents said they'd be interested in switching to a bank that offers app features they think are missing. Credit unions that serve the east and west coasts are particularly vulnerable, according to the data, because 58% of the people willing to switch live there.

Notably, mobile app use is not replacing branch visits quite yet. Though 88% of respondents said they use a mobile banking app at least weekly, a whopping 69% also said they have gone to a branch at least once in the last 30 days, according to SNL.

Bank of America, Chase, Wells Fargo and US Bank still dominate the market, with 45% of all respondents using at least one of their apps, according to SNL's list of the 30 apps with the most users. Navy Federal Credit Union and America First Credit Union were also on the list, though both ranked at or below 1% market share. Navy Federal has $68 billion in assets and 5.4 million members; America First has $6.8 billion in assets and about 700,000 members.

The west coast tends to have more credit union-based mobile app users, with Boeing Employees Credit Union, Navy Federal, Golden 1 Credit Union, SchoolsFirst Federal Credit Union, BECU, First Tech Federal Credit Union and Alaska USA Federal Credit Union all appearing on the list of 22 mobile banking apps with the most users in that region.

Respondents who don't use mobile banking apps – two-thirds of whom are over 48 years old – said security is their biggest reason for avoiding mobile apps, and about 40% said they already do the work on a desktop or laptop. About one in five said they just don't see the benefit.