That's the only known issue and in all my tests, with the fix applied, it works fine (J2.5 and J3.0). Menu item protection does not hide the menu item. It protects the destination so the link must be clicked for it to begin protecting. Menu protection is also purely Itemid based so you may want to use By URL Part instead. It's also possible to set Usergroups to ignore the protection within CBSubs > Settings > Integrations > Content/Extensions; ensure you didn't set everyone to ignore its protection. Also ensure the CBSubs Bot is installed, enabled, and public as without it CBSubs Content will do nothing.