There are two tiers - the more you pay, the more expensive the cars you have access to. So it's somewhere between a conventional lease deal and a car club.
What's in it for you, then? Well, it depends who you are. If it's for you, I guess you'll know it. You can have a car that suits your needs, when it suits your needs. If you live in town, are short of parking space and they charge you a fortune for a parking permit, it's ideal. You can still have a practical car and a sports car, which could be beyond you otherwise. Only one at a time, but it's not like you can drive two cars at once anyway. I can see why you would.
Then, I can see why you wouldn't. Not just because, presumably, there won't be a 718 Cayman for everyone and a driver to swap them all at the same time; so if you all want one at once, on a Friday afternoon before a bank holiday, you might be out of luck. I suppose we'll find out how that goes, though.
So what's in it for Porsche? For one it's broadening its appeal: there will be those who won't buy a Porsche who'll sign up for this. But even where Porsche is talking to people it already knows, there are advantages.
Demand for used cars is, generally, higher than it is for new cars, and even though Porsche doesn't suffer from oversupply like mainstream car makers, I suspect it'll quite like to have a decent supply of used stock. Mainstream car makers find myriad and devious ways of getting new cars quickly onto the used market - massive fleet discounts, pre-registration, giving dealers big bonuses to find cars homes - which isn't an option easily open to a premium brand.
So why might this not be the start of something revolutionary within the industry? I don't doubt car sharing will increase, but it won't be like this. Why not? Because they can't do it. Some car makers don't have a big enough range, some others aren't appealing enough, and profit margins are too small to lay on what is a personnel-heavy scheme. Do you fancy swapping the Jazz for a CR-V this weekend, darling? Frankly, dear, I don't give a monkey's.
So it's not for everyone. That much is true for potential buyers. But, I suspect, it's even truer for manufacturers.