Kha'Zix is very popular champion among our elo boosters.
This guide is approved!

"I find the slight mobility boost to be extremely beneficial, and it allows for more pots than Blade or Long Sword does."

Doesn't mean it provides you more sustain. You siad you want to evolve Q first in lane to improve your trading potential which would be weaker due to Boots.

"I also don't really like LW on Kha, because I tend to build him more bruiser than I do assassin."

Often just one out of three offense items - you're doing the same things and it's one of the most effective ones.

"This is a build made specifically for a friend, and if it does get views, cool."

Then make it private, you can archive it it can still show the link to him ...

I respectfully and wholeheartedly disagree.
I find the slight mobility boost to be extremely beneficial, and it allows for more pots than Blade or Long Sword does.
I also don't really like LW on Kha, because I tend to build him more bruiser than I do assassin.

And since the nerf that makes it a 2 second re-cast time, evolving R first is basically useless to me. This is a build made specifically for a friend, and if it does get views, cool. But for me, Q and E are my go-to evolves, no matter the situation. I take R if I'm being beaten in lane

No mention of Last Whisper anywhere, no Runes and Masteries shown for the jungle build, you should evolve Void Assault first in every situation, starting boots is poor, Doran's Blade and Long Sword are way better, rushing Hydra on top lane Kha seems to be rather okay but for the jungle you ditch this items generally, Masteries should be 21/9/0.