I've never seen Prime as a purely money-saving scheme. It possibly does save me a bit overall (but not every month, for sure) on the things I genuinely want next day, but I also get the convenience of weekend delivery which either isn't available or is very expensive without Prime (from Amazon or other options), or certain drop-site delivery locations that don't seem to be available & cost-less without Prime. There is also the utility value of not needing to think about delivery as much.

> designed to get you to spend money at Amazon.

That much is certainly true. But it doesn't have to cost you more that way than it would anyway.

> You just need to do the sums.

Shopping around can be time-consuming, especially as every other retailer is pulling similar tricks so you have to make an effort to see through their crack as well. Though I do sometimes double-check and find the Amazon price the same once delivery is accounted for in both cases. Sometimes there is a saving to be made. Sometimes that saving has a convenience cost.

> Another common defence we will see when people respond to this is "Oh I know it doesn't save me money, it's the convenience".

Is paying for convenience inherently wrong in your world view?

IMO, spending time and/or cognitive effort to save money has to be weighed against what-ever else you might be doing with that time/effort (going out for a run, playing with the cat, doing some work, just enjoying doing nothing really, ...) otherwise you are guilty of exactly the same sort of false economy.