Once you reach level 40 you realize that God mode does not work, but that was to be expected. Being only visual, it can be a disadvantage to use it, as you can't find the best area to farm exp while AFK. You might leave your hero around mobs that hit hard, and if you return to the game in 30 minutes, you are dead.
As far as the speed multiplier goes, in many cases, it is actually a disadvantage to use it. If you look closely, in many instances, you will see the animation gets a speed up, but the actual number of damage ticks floating on top of a mob does not increase. You look like shooting 2 or 20 times faster but the server registers the regular number of attacks per second. Furthermore, some skills produce increased damage continuously for a number of seconds, the animation speeds up but the duration of the skill gets reduced so, during a longer fight, you end up doing LESS damage with the speed multiplier. This would even out if the attack speedup would influence skill cooldowns, but it does not.
Just enter the trials, you will get much better results without the attack speedup.
I think that any skill over time gets nerfed too much by the speed up, if there is a class that has only instant skills then saving time on the animation might prove to be an advantage. So far, I have tried only the marksman with wildpack specialization. Unfortunately, I can't benefit from the animation speed up.
What works beautifully and it provides an advantage are the walk on air and the attack range increase. What does not work, is attacking strong elites or bosses from up in the air, they ultimately kill you nonetheless, even if you look like being very far from them.