You don't have to, but for not to be tempted using dmg multiplier, I personally will use original/official apk.
I think you knew already, but I will say to people who don't know.
The Arena is not all about how fast you can complete a stage, it is about how much damage you deal to enemies, which result in points that will gets you to leaderboard.
So, be cautious using dmg multiplier (or don't use it at all), don't be greedy, you don't want your time be wasted on this, time is precious!