Point-of-sale lender Afterpay reports it has 1.5 million U.S.customers, a milestone it’s achieved by embedding itself into the payment platforms of large consumer brands.

The Australian company this week added known brands like Ray-Ban, O’Neill and Levi’s to its partnerships with 3,300 retailers — a beachhead in a crowded market of startups that include Affirm, Klarna and Splitit. “[Customers] are showing how important it is to them to be able to manage their budgets responsibly and never be caught off guard by surprise interest payments or fees,” CEO and co-founder Nick Molnar said in a statement.

Afterpay’s repayment model lets customers pay for purchases in four biweekly installments, without paying anything upfront. The company says it doesn’t charge interest on the loans, but it charges an $8 late fee for missed payments, capping late fees at 25% of the purchase total.

Despite the reported growth in the U.S., many questions surround the numbers. Jen Redding, a senior analyst at advisory firm Wedbush Securities, said Afterpay has increased retail conversion rates, or the number of people who go to a retailer’s website and actually buy something, by 30%. Whether this growth is sustainable, however, is unclear, she added.

“If numbers go down quick, it means they’ve made a bunch of bad loans,” Redding said in an interview with Bank Innovation. “If those numbers don’t rebound, Afterpay has a real problem.”

Despite these risks, Afterpay offers value to retailers because it helps them drive conversions without letting them take on the risk, Redding said. The company charges retailers 4-6%, while credit cards typically charge around 2%.

The point-of-sale loan model also has attracted the attention of big-box retailers like Walmart, which recently enabled point-of-sale loans at checkout through a partnership with startup Affirm.