Often when explaining koinos's mana system, people will focus on the fact that there is a cost. It's not truly free.
You're paying in opportunity cost. If you choose to do one thing with your mana, you might not have enough to do something else you also wanted to do. This is why we use the terms fee-less and free-to-use. There's no monetary fee, but there is a resource cost.
Some people look at this and get hung up on the fact that you're paying with time. After all, time is money... Right?
Well, yes, but only if we're talking about your time. You can spend your time to make more money or you can use your money to buy more time (by outsourcing a job). There's two big differences between your time and mana.
First, your time doesn't regenerate. If you spend the day working, then you can't also spend that time going on a picnic. The amount of time you have available in your life is decreasing constantly, and you can't get it back. Mana is constantly recharging after you use it.
Second, you can use mana instantly. With your time, you actually have to spend it. You can't use it any faster. You can spend all your mana as rapidly as you want. This is actually an advantage because you can get the outcome you want instantly.
So, no time isn't exactly money. Owning Koin is like owning an army of lightning fast robots. You use their time to do things for you. You don't have to spend your own time.
P.S. sorry if that got a little depressing in the middle 😅