I have a Curve card, which is essentially this. I paid for the beta and got a free wallet out of it (a nice Tumi one) and £50 in reward points so overall I've actually profited from it. There isn't a monthly charge (yet). Curve is a prepaid Mastercard that acts as a middle man. You spend, it charges whichever card is currently selected. You get extra benefits like zero fees abroad, cash withdrawals, etc.

There is also a reward program which is OK if you shop at the places where you get points, but it's no different to signing your card up to a cashback program like Quidco. There are a few big names like Boots, Waterstones and B&Q where I go reasonably often. https://www.imaginecurve.com/curve-rewards-web/

The main advantage to me is security. If your card gets stolen, you can revoke it within minutes without worrying about someone having access to your debit card. Because it's linked to the app, you can see immediately when transactions happen. You can do the same with a debit card of course, but it's an added layer of obfuscation.

Originally it was supposed to be an amazing loophole for American Express users. You could spend Amex everywhere including on cash withdrawals and rack up points like nobody's business. Then Amex pulled out, so that was a bummer. A lot of people on HeadForPoints got very annoyed and felt like they'd been suckered in. To be fair to Curve, they compensated everyone.

I believe you can still use it to withdraw cash on credit cards though, so there's still a way to manufacture points spend.

I use mine daily and while it's fine 95% of the time, there have been sporadic occasions where it's been declined. You can't use it at pay-at-pump petrol stations, for instance. It's not reliable enough yet that I can go around with only a single card in my wallet (which sort of ruins the idea of it). It's really useful for traveling abroad though.

So, for reference, I'm a guy who has multiple cards. I have two debit cards and a credit card.

The credit card is a credit card (and I mostly use it for company purchases that get reimbursed).

The two debit cards correspond to two different checking accounts. I have a "main" checking account that my check gets deposited into, and another account that I use for, mainly, online purchases or recurring subscriptions like netflix or anything where I am worried about card security. I transfer money into the account, then make the purchase, never leaving more than a hundred bucks or so floating in the account. That way, I limit my own pain in the event that someone gets hacked or my card gets leaked online - I'd much rather not be able to pay netflix than not be able to pay rent.

At one point, I also had a home depot card when my wife and I were fixing up our house in preparation to sell it.

I have a wallet that functions effectively as my phone case and wallet in one, and reducing the number of cards I have to carry around to - potentially - drivers' license, one payment card, and clipper card would be fantastic.

My dream for something like this is having everything on one card would let you manage the complexity a lot better.

Having one single interface to pay all bills and see spending breakdowns aggregated across all your cards, recommending the optimal order to pay down cards (if you are going to carry a balance).

Then on top of this, automatic fallback in case one card is declined, new numbers for every online transaction (not tied to a single provider).

You could even layer on top a simple scripting language to choose the card to be used for a given transaction. E.g. Use my rewards card when buying gas, but if I've maxed out the points then use the lowest interest card. Or round robin the cards to spread out the balance.

Or imagine a group outing where everyone can all combine into a single virtual card, with the ability to distribute charges however you want on the back end.

There are a ton of cool possibilities available (albeit very challenging to get right). And in theory, many people have at least 2 cards for redundancy purposes. Add in no fee rewards cards (Target, etc) and it will add up even for non hardcore points collectors.

> It's nice to have one card as a backup, and some hardcore churners / points collectors are going to want 5 or 6 cards and use different cards for different categories... but they're real niches, it's not something that a mainstream, mass market consumer is going to want to manage.

I don't think this is the case. I think the average person has several credit cards (and is probably in the red on all of them).

On the other end of the spectrum is the financial-savvy user that also has multiple credit cards: One that gives them a gas discount, one for their Costco membership, one for restaurant cash-back, one for general purpose cash-back, one that waives the foreign currency conversion fee, etc.

> having many credit cards is a complete pain to manage, because for each card you need to [...] change the address when you move

Why? I did that once, and it was a huge pain. But the cards work just as well no matter what they think your address of record is. Now I just don't change it.

What I don't understand is the need for multiple credit cards. I have a bank card (an EC-card) and I haven't used my credit-card since a month (other than automatic transactions).