When you jungle with Rengar, you must be carefull to map always like other junglers. But you should beaware to going ganks before lvl 6 becouse they migth have warded or saw you smth smth else... That's why your ulti is just rigth thing to jungle. You can use it before ganks to not to be seen or regenarating ferocity before gank.

Pros Cons
*It can be very easy to take kills in team figth with Q. *You are the first one gonna be
*You can last longer with Guardian Angel and your ulti. atacked.
*He is the very best hunter. *You can 2v2 lane easily.