Yes, it's only useful for apps with a subscription or in in app...

Yes, it's only useful for apps with a subscription or in in app purchases paid via the store and even then only the grossing ranks are useful, not the download ranks.

Trying to assess something like after pay is pointless because it's revenue comes from outside the store.

However, this method is very helpful to monitor growth and simply to give insight on what's hot, mediocre or just a flop.

We were lucky early on with mwr in the respect that it was contained to 1 or 2 countries and just 1 app receiving all of its watch related residual income through the app stores and the set monthly income directly correlated to watch sales, so it was quite effective, but also very rare to have that. It's getting more complicated now.