This is the first I've heard of Delayed Gratification. That's a hefty subscription price -- is that their main source of revenue?

It appears they get their money from subscriptions, yes. There aren't any ads in the magazine. They also do some classes on how to make infographics and write articles.

Is it that hefty? I'm seeing a price of 55 GBP for the US.

Works out to almost $20 per issue for a quarterly. So it's a lot more per issue than Time. Not saying it's not worth it. (Time is for dentists' offices and bird cages.) My comment about cost isn't a gripe, just an observation about their business model. It takes real belief in your product to charge that much for writing, when we're so used to getting it for free.