Is EtreCheck safe? I thought it used to be in the Mac App Store, not there now.

EtreCheck is perfectly safe. Just because an app is in the App Store is no guarantee it is safe. One of the least safe apps you can install on a Mac is in the App Store.

Wisdom of the crowd says that EtreCheck is safe.

Also exiftool is safe. "but it’s unsigned, and if you have the OS X default settings on, you’ll get the error “ExifTool can’t be opened because it is from an unidentified developer,” [...] you can install individual applications in the future by control-clicking the installer and selecting Open."

https://news.softpedia.com/news/Fix-OS-X-Error-Application-Can-t-Be-Opened-Because-it-Is-from-an-Unidentified-Developer-407375.shtml

Two cents here.

Certain Applications maybe available on the Apple Apps Store - this only means the Developer is prepared to pay Apple a portion on each sale.

What the Application may do to the computer is up to the User to check this out before purchase.

Prime exempt of available on the Apple Apps Store - CleanMyMac but never every download and install this piece of " Stuff "

Best diagnostic tool out there, 100% safe.

I understand its developer decided to discontinue the Mac App Store version because Apple's requirements would impose unacceptable limitations in its capabilities.

It is merely a data-gathering and reporting tool that does not alter a Mac in any way, and last I checked its developer even made its source code available for public scrutiny. Things don't get more transparent than that.