My mobile provider charges a ridiculous amount per mb while the price in a subscription is much cheaper, if you don’t use more nor less of the allocated amount. So even though they provide both options you mentioned, neither feels ethical to me.

Edit: 1 eur per 10mb in the prepaid version vs 13.50 eur per month for 2gb plus other stuff like calls and sms. So I either have to waste money on stuff I don’t use every month or pay 15 times more for the same service