is rengar worth buying?

Someone will post and say yes.

Someone will post and say no.

I will ask you if you have fun playing him, then reply with the same answer.

If you think you're going to be Dandy, no because Dandy has a team, You don't.

If you understand how Rengar works and what his real major strength is (stun from stealth, not QQQQ gib, thats almost useless) and use that to snowball teams effectively, yes he's worth it,