I would stick to using Apple Apps for this to avoid getting dinged for a terms of service / license violation. 

> - Manipulating play counts, downloads, ratings, or reviews via any means — such as (i) using a bot, script, or automated process

> - You may access our Services only using Apple’s software, and may not modify or use modified versions of such software.

https://www.apple.com/legal/internet-services/itunes/

Once you’ve downloaded if using Apple’s software you should be clear to analyze it as long as you’re not further distributing it or using the app should you choose to alter or change it and not just learning how it was assembled.