One of TransferWise's distinguishing features has been its ability to think just big enough. Without sufficient scale, the company could never have built such a successful money transfer business. Yet it also didn't expand too quickly, instead focusing on a core online international money transfer service (available in 50 currencies), from which it takes a commission using the interbank mid exchange rate, which is fixed for two days to avoid any unpleasant surprises.

TransferWise's service is popular because it is considerably cheaper than using a bank. The company charges about 1% per transaction while many banks charge 3-5%.

TransferWise can charge customers less because its business model doesn't require the money to actually be sent overseas. For instance, if a mother in the U.S. wants to send US$1,000 to her son in the UK, she first sends it to TransferWise from her TransferWise account. The company then sends the equivalent in British pounds from a TransferWise bank account in the UK to her son's own bank account.

Overall, TransferWise has about US$2.5 billion in customer deposits, 8 million customers, and does US$5 billion in monthly cross-border transactions. 

In early July, TransferWise said that it had secured a license from UK regulators that will allow it to offer investment products in the future. The investment products will reportedly be of a passive nature and come from third-party providers. However, the company does not plan on segueing from investment products into full-fledged banking.

"The only thing that the banking license in Europe lets banks do is lend out the deposits that customers give them, and that’s not what our customers are asking for," co-founder and current CEO Kristo Käärmann told Tech Crunch.