Not many banks have a cult following. Monzo is a rare exception.

More than 100,000 Brits have signed up for the smartphone bank that claims it will revolutionize banking.

Several mobile-only banks have been launched in the U.K., including Atom and Tandem, but Monzo has quickly become the most popular.

Monzo was founded two years ago by Tom Blomfield, a former Oxford law student who had previously co-founded GoCardless, a direct debit provider.

Deeply frustrated with traditional banks, he decided he could do better.

Blomfield said his cards would be blocked when he made payments abroad -- even though he had told his bank he was going on holiday. Fees were charged for cash withdrawals overseas, or for overdrafts he knew nothing about. And when his bank was suffering problems with its systems, there was a lack of communication.

"It's just amazing that there's literally so much control and power at our fingertips and banking hasn't really adopted any of that," he said.

Monzo offers something rather different to main street banks and their digital offshoots. It sends you a notification every time you make a purchase, and won't charge you when you travel.

Exchanged £90 at the post office and got €90.

Paid for a €93 @Deliveroo whilst in Berlin and @monzo charged £79.



YES, MONZO LAD 🤜🏼 — Emma Ware (@EmmaCWare) February 13, 2017

It allows you to track purchases in real time, temporarily freeze your card if you've lost it and help you stick to a strict monthly budget.

Everything Monzo does seems like a no-brainer. Blomfield says that's because he had no experience in traditional banking.

"Having the baggage of experience sometimes is a hindrance because you have this fairly rigid view of the status quo. (Monzo) started from scratch, so there's almost a value in that naivity and not having any preconceptions," he said.

For now, Monzo's limited banking license (granted in August 2016) only allows it to support pre-paid Mastercards that you have to top up using Apple pay or a bank transfer.

But Blomfield expects the restrictions to be lifted "very shortly." This would allow Monzo to offer classic checking accounts, starting in the next few months.

Despite the limited services, Monzo is generating an enthusiastic following on social media.

Recently signed up with challenger bank @Monzo - loving the simplicity and UX already — Francesca Russell (@FranRussel1) February 24, 2017

First month using @monzo and I'm far too excited to manage my banking #amianadultyet ?💳 — Alice Wells (@wellsalice) February 23, 2017

By being open about how it develops its product, Blomfield says Monzo has been able to create a product people actually enjoy using and find valuable enough to tell their friends about it.

"It's a virtuous cycle of reinforcement," he said.

To avoid being overwhelmed, the startup makes new customers wait a week for their hot coral debit cards.

Monzo has yet to make a profit. But Blomfield says he expects that will change when it's able to offer full bank accounts -- particularly from overdrafts.

"Monzo will tell you up front even before you've overdrawn that you're running out of cash. It'll tell you: Here's how much it'll cost you if you borrow -- you'll never be charged more than X pounds. Do you want to take this, yes or no?"

@ianjamescox The second @monzo current accounts become available I'm switching. App, customer support is light years ahead of current banks — Callum Strong (@csscallum) February 23, 2017

Blomfield's plan doesn't end with checking accounts. Ultimately he wants Monzo to allow users to file expense reports to their employers, split bills with their partner or roommates, and even check whether they're getting the best deal on gas and electricity -- all within one app.