Netguard [1] is a loopback firewall (installs as a local VPN) that doubles as an adblocker if you install the version from github [2]. I installed from the play store and used the IAP to contribute to development before swapping to the github version (the version on the play store can't block ads [3] due to it being a ToS violation)
Note that one of the recent updates [4] introduces ads for the free version. But not if you buy any of the pro features. Seems a fair trade, plus it's open source (which makes me slightly happier about routing all network traffic through it)