Im lvl 63 now and I started to play with mod from the lvl 1, at start I used only x3 dmg s def and then I abused X10 in events(where are no leaderboards), bosses etc... still not banned.
Updated:But you have to know when to abuse and when not, I maxed 3 main heroes with 16-18K power each so yeah I can permit myself but if ur lvl 10-20 better still slow with x3 and then you can slowly start to greed.