Kha'Zix evolving his ability Void Assault at level 6 is quite the rare sight seeing as it not even being done 2% of the time on EUW however, this is far stronger than one would suspect.
Currently, Kha'zix's most popular ability to evolve is Taste Their Fear which increases the range of Taste Their Fear and Kha'zix's basic attacks by 50. If the target is isolated, it refunds 60% of Taste Their Fear's cooldown. Now I know what you're thinking, how can you give up such a strong ability so early on? Void Assault allows Kha'Zix to passively gain Void Assault for 2.5 seconds in a brush. This persists for up to 1.25 seconds after exiting the brush with a 10 second cooldown per brush cooldown. This allows Kha'Zix to roam around the map at such a quick pace and increases his ganking potential massively.
Being able to have this passive stack with top and bottom lane's brushes means that unless the far brush is warded (which might not be likely for those unaware of this), Kha'Zix can get behind the enemy laner/s and ping them with Unseen Threat freely to slow the target. Some help from his laners and the targets can consider themselves obliterated, sending them back to the fountain.
Taste The Fear heavily scales since isolated targets receive a huge amount of bonus damage and the original damage scales with 140% of bonus attack damage. Because of this, it doesn't massively affect Kha'Zix to abuse the fact that the evolution of Void Assault is so potent early on and take the Taste Their Fear evolution second when you have a huge more amount of bonus attack damage. The downside to this, however, is that you deny yourself from having your leap evolved early on so you won't be getting any resets for a while.
Overall it does come down to playstyle however, I would hugely recommend to the jungle mains to try Kha'Zix with the Evolution path of R>Q>E as it is well able to be abused when played correctly.