We've got two options for Closers. Both of them use XIGNCODE3 anti-cheat (digital AIDS), which is known to cause performance issues.

Closers Online (retail)
https://www.closersonline.com/
https://store.steampowered.com/app/215830/Closers/
>need to make a Naddic account regardless of version (steam/website)
>leveling trivialized to rush you to endgame
>Steam version has a free DLC with some 7 day premium things
Patching took ~10 minutes

CODE: Closers
https://codeclosers.to/
https://union.codeclosers.to/
>3x exp/drops/credits
>reduced p2w elements
>character balance changes
>several guides on their forums
>has almost as much content as the KR version (EN retail is behind)
>apparently the translation is rough
>anti-aliasing is disabled for some reason
Patching took ~30 minutes. The patcher would randomly fail and require a relaunch, so keep an eye on it. Running it as admin or adding the folder/exe as an exception in your antivirus might help.
https://union.codeclosers.to/index.php?/topic/2215-launcher-problem-repair-process-failed/#comment-11642