It is experiemntal because Windows doesn't officially provide a way to change default file manager, and it will always be experimental feature (because WIndows itself is held by duct tape and chewing gum and it is so easy to break).
The biggest risk is not being able to open Explorer again. This will only properly work if you never had other file managers installed and set as default; otherwise there is no way to know what will break as many file managers set wrong registry keys and then when OC sets itself as default, Windows for some reason forgets how to even open Explorer even when OC restores changed registry keys to their original state.
Before doing it:
1. Learn how to backup and restore Windows Registry, just in case
2. Create system restore point
To revert, unchecking that same option will revert the two registry keys that made OC default.
As a backup, you would copy "RestoreExplorerAsTheDefaultFileManager.reg" from OC install folder onto desktop in case you need to run it.
But this is all I can tell you. Windows doesn't provide a "safe" way to change the default file manager, so you would need to know how to restore the registry if something breaks. Note that there is no support of recovery, because if something breaks there is no way of knowing what other registry keys in anyone's Windows registry are set.
Also note that OC doesn't replace system Open/Save dialogs, as nothing can replace those - it just sets itself to open folders for programs that support it.