Challenger banks have reshaped the customer experience across financial services, drawing in consumers and investors alike, but that might not be enough to guarantee their economic viability .

Profitability will likely come down to challenger banks’ product expansion, which would ultimately lead to cross-selling opportunities, according to fresh research from CB Insights released yesterday.

“Customer experience will be key to retention, as well as the ability to cross-sell new products to customers and enhance the customer lifetime value across the duration of the banking relationship,” the report read. “While [challenger banks] have reshaped customer expectations, the economic viability of these businesses is still up for debate.”

Indeed, challenger banks are some of the world’s fastest-growing companies. Brazil-based Nubank, a challenger bank and credit card issuer, more than doubled its customer base year over year to 30 million in September. Chime, the largest U.S.-based challenger bank, also doubled its customer base year over year to north of 10 million customers in September, and New-York based Current reported it was adding 100,000 users per month in the second quarter and expects to reach 2 million users by yearend.

For that usage to translate to dollars, challenger banks are expanding beyond their initial product offerings, the report noted.

Micro-investing platforms Stash and Acorns have expanded into mobile banking, personal finance management, and auto-investing and brokerage. Dave, which originally offered overdraft protection, has moved into cash advances, early pay access, mobile banking and early pay access. MoneyLion, initially in the game with a personal loan product, has ballooned into high-yield savings accounts, personal loans, rewards programs and credit cards.

But as challenger banks seek ways to profitability through expanded offerings, they have ironically begun to look more like the traditional banks from which they once strived to differentiate themselves.

“Venture-backed startups have sought to unbundle banks following the financial crisis. Now, they are in many ways rebundling a suite of products to resemble a digitally-native, full-service bank,” according to CB Insights.