Ostensibly, it's a place where multiple people sign up to buy something, so that you get bulk prices. In my experience it's been much more about trying to get you to buy for the same or more than you can get on Amazon using 'limited time' artificial scarcity.
For things like sewing equipment or knives, what you describe is true, but for things like custom keyboards, it is not.
For instance, I purchased an Ergodox on Massdrop for less than $300 at a time where sourcing the pieces yourself would have cost well over $1000.