Due to the way Rumble's Equalizer (and Viktor's Death Ray) are cast, they have much greater flexibility in position than skills like Jinx's Flamechompers, Malzahar's Call of the Void, or Anivia's Crystallize have. While many lane skills can only be placed parallel or perpendicular to the champion, Rumble's Equalizer and Viktor's Death Ray can be positioned in any angle around them, which allows them to better place the ability to hit more targets or block off sections of the map from a much greater range.
It helps with you don't smartcast Rumble's Equalizer or Viktor's Death Ray until you are more experienced with the skills.
And, to be honest, Rumble's ultimate isn't really that hard to use. It's a little tricky the first few casts, but it's really easy when you've figured out the trick behind it. Just take Rumble or Viktor to a custom game, rush some CDR and practice casting the skill until your figure it out. It should only take a few minutes.