I did use damage multiplier and still fine, i'm on stage 13-15 cheating from the start, didn't get banned yet on this account yet.
What i did noteced is: don't do steges if you power is too low compered to the stege power recommentation, most accounts that i tested iginoring the stege recommendation power level got banned.
And i don't if is power level is red, i mean if you have 15000 power and the stege recommends 25000, if youre 2000~3000 below it's probaly fine
So use the mod to facilitate your grind, not to do it all stages, yeah sure you will not be able to get to the last stage in tha same day, but you will probaly keep your account
(I belive the reason that you're didn't get banned is becuse both +Crits and infinite ammo does not make possible you clear maps above your power, only makes easier to clear maps within your power level)