How hard is rengar to learn

So yes I know mastering rengar is hard. I played him the other day for fun and oneshoted everyone and actually managed to get all 5 stacks but I wasn't as aggressive about it like I usually am. So the lethality changes were an indirect buff to assassin rengar. Not sure if tank rengar is still good and haven't tried it yet. This is focusing on ad rengar. So early ganks are kind of meh even with the ebola strike because the ferocity has a time limit. Last season was build up 5 stacks and gank. Now you can't. Also he's permmabanned in high elo. The lvl 6 gank almost always works for me then I try to get some trophies. I've kind of changed my playstyle to not be so active about it. I know he is feast or famine but as long as you don't feed and you get a kill by lvl 6 without dying too much, you should be fine. His w is a roar which heals when empowered fro monsters but I don't think it matters vs champions and the free cc shield is getting removed. Unfortunate for the rengar one trick ponies. It's basically the arhi charm/ pre rework ryze nerfs where they made the passive have a charge system while active and they made the charm not stop dashes. This is actually a little bigger IMO but I don't use it since I don't remember but I will use the eon if I buy one since it's easier to remember. The q is easy enough to use. If you let your guard down, it can mess up the ult but I try to keep that in mind. I occasionally play eve in normals for fun. So how hard is rengar to learn and do good with.