Depending on how much time you have, some of those features can save you a bit. Not sure how that compares to other widgets like itch.io though.
Even scrolling through my GOG collection of games I'm somehow too lazy to play instills in me a sense of pride that at least they weren't purchased on Steam.
Though there are also major practical advantages of purchasing things within stores like GOG and Steam instead of a bunch of disparate websites: when you move to a new computer, you don't have to chase down a bunch of websites and license keys and emails to reinstall all of your software. Which is something I hate so much I only got outside of platform shops as a last resort.
If the product payments are typically below $10 then it makes sense to use Humble.
Trying to figure out which county in some state you owe $0.14 to is a nightmare.
Five percent seems like quite a lot, given that most payment processors charge less than three percent. What sort of value do they add outside of payment processing?