Pay-to-play model. "Keys" are needed to unlock each short chapter per game. The spend rate greatly outpaces regenen rate, driving f2p users to watch ads to speed up key acquisition. Then they cap the # of ads/day. Price per key is disproportionate to play time. Gameplay is average quality. Overall impresion is this app is another disapointing microtransaction revenue engine. Devs are doing decent work but the business model is insulting to users.