Not sure about y'all, but for me I only have one version of the game in my library. The image says Agony unrated, but the name of the game in the library, as well as the executable, just say Agony, and the install folder is titled AgonyLegacy. Don't see anything about it in the configuration menu. How do I know which version I'm playing, and how do I switch between the two?

There should be two seperate games in your library. However, if you use Galaxy, it only shows one.

If you want to be sure just use the backup installers from GOGs page.

Isn't the easiest way to see if it's the unrated version just to fire up the game and look down? If there's a penis then it's unrated.

I believe you're half correct. I checked on my browser and they're both there as seperate games. I installed Agony Unrated via the offline installer and there's a few notable differences between the version Galaxy installed. The offline version is slightly larger, the install folder was Agony, while the galaxy install folder was AgonyLegacy, and Galaxy immediately recognized the offline install as Agony Unrated, which it treated as a seperate game to the Agony version it installed. Also, most importantly, when I booted up the Galaxy install, the title page said Agony. When I booted up the offline Unrated install, the title page said Agony Unrated. So at this point I'm pretty confident the version that shows up on/is installed with Galaxy is NOT the unrated version. To install the unrated version (at time of writing) you must do so through gog.com

Thanks for the help everyone. Would be nice if Galaxy just had both versions listed, hopefully that'll be fixed at some point.

No, you don't have to use the offline installer. Just select the prefered version on the Galaxy game page and install it. Look at the attached screenshot.

Main menu. The succubus mode is unlocked from the beginning in the unrated version.