This sort of thing isn't often needed but when you need it, you need a good one.
I tested this one out of curiosity some time back - probably a year or so ago.
It's not snake oil and in my opinion the dev is honest and conscientious.
However - this app and any like it (I'm not sure off the top of my head if there really are, but Clean Master (don't install this) will do the orphan cleaning too) - are deceptively powerful.
And the SD Maid dev tries to warn about that but too few people read the label before use.
If it glitches evaluating what's safe to clean, things will break in a hurry.
Not the dev's fault, it's hard to make this sort of thing perfectly universal.
I advise a good, as-complete-as-possible backup before use - that's apps, data, internal storage and sd card.
I'll bet most people will be ok but backups are easy and there's no reason to not protect yourself.
On a well behaved phone, SD Maid doesn't need to run often.
On a very well behaved phone, you may not notice a difference.
But it's a good app for what it is, so fwiw, I recommend it - provided you do a backup and read - not skim, read - what the dev has to say before use.
