There is always a chance of getting banned when using GM Cheems (or any other cheat). Safety is never guaranteed!
You have been warned.
Don't cheat on accounts you're not willing to lose
Always use GM Cheems with alt accounts you're willing to lose. Always install it on a separate Chrome profile and only log in to your alt accounts on that profile.
You don't want to be in a situation where you have GM Cheems installed and you're logged in on an account you're not willing to lose, even if you don't cheat. Simply having it installed and being logged in to your account on the same Chrome profile will make you suspect.