I'm not sure what the F-Droid devs' stance is on this sort of thing. If it is the client app it would violate Google's ToS.
If that app is indeed a fork and using adds, its violating both, ourfdroidclient license (since they dont provide the source code fortheir ad-modifications) and Google's ToS which have a non-compete/ no-appstore clause.
For all of you who have a Google account, please flag this as inappropriate using the link on bottom of the Play Store page:
I'm comparing the code in it to see if it might also be malware.