[noob question] Reasons for using service like PlayHaven for IAP?

Hi, 

 I’m planning on adding in-app purchasable goods to my game (extra game mode, some ‘boosts’, and the game-currency). I can do that using the standard in-app module. But then there are some services, like PH, that also cover those. 

 So my question is - what are the PROS and CONS of using those? Is it something better working for the users (huge diff)? Or less code to write on my side (little diff for me)? Or easier management of those IAPs? Or, some user interface for the “store” already done?