Android in app purchase free games are absent of in game payment models. An exception to the rule are games that are marked in the Google Play Store as having in app purchases but only have a singular link to donate.
Games that are absent of in app payments are reminiscent of the older type of payment model for games where a consumer pays upfront once for the entirety of a games content. Many gamers still consider this to be the only honest way to sell a game even though there are some perfectly fine exceptions where a full game is sold through an in app purchase or cosmetics are the only thing sold to support a free title.
With the befuddlement by Google for allowing an easily navigated storefront it can be difficult to find games that are in app purchase free and so this pro/con comparison is meant as a resource and tool to find and recommend the better of those types of games.