comikey is one of the worst services i've ever seen. it's on par with many mobile and multiplayer games shops these days. you need to unlock chapters (even short .5 chapters) with like 3 keys and you need to pay 2 Euro to get 20 keys but the whoole translation between digital currency at odd rations make you loose sight of how much money you're actually paying each time. and then they add some extra currency that comes with higher payment options, but that extra currency only lasts 5 days, so it forces you to essentially spend your money quickly.
it's sad such a platform is slowly taking over many good series.