Experience with Addons Detector program

I've used Addons Detector. It was handy back when push advertising add-ons started to appear. These days those particular add-ons are banned from the Play Store, so if you get your apps from there you should never encounter them. I've still got it installed, occasionally use it to investigate permissions. It's harmless.

In-app purchases just means that you can pay to unlock a feature or remove ads, if you want (I don't recall ever seeing ads, but I've had it installed for so long that I can't recall whether I ever paid anything).