What can you tell me about DFNDR?

And once I do the sweep, a dozen adds come up. Is this a worrhwhile tool or a scam?

This reddit site is talking about the same thing.
It seems to be a scam. Anything that spams you with ads should definitely not be used. use AVG or any other verified antivirus.
As a user in the reddit thread says, antivirus isn’t really needed on android.

Here’s a link incase you can’t uninstall it.

There are so many downloads showing for this app meaning so many are suffering due to this. Interesting thing I noted that for every comment it was showing “for an older version”. I guess users have now started complaining due to which they want to confuse new users to think that the issue is related to old version of the app and not the latest one..)