MarsHall
So it has 4 tabs at the bottom that are different features.
From what I used, the main one is Similars.
You tap on Smart Cleanup and it’ll automatically mark all your similar images for deletion.
That’s really what this app is best at. I was able to remove about 800 similar photos (that’s like 4 GB right there).
And before anyone says you can just do that in the Duplicates album in Photos... forget it.
I checked Duplicates only showed like 20 photos for me.
(It only catches exact copies, not similar shots like these apps do.)
After that, I went to the Screenshots tab and deleted all my screenshots.
Your iPhone can do that too, so not gonna lie there.
Then I used Heavies, it shows your largest files. I deleted a couple of old videos here.
This feature basically exists to sort your files by size, because again, Photos doesn’t let you do that.
There’s also a Lives tab that compresses Live Photos into stills, but I didn’t use that one.
Anyway, it’s pretty simple once you open it. You’ll see what I mean.