Hello.

So, does hbao+ really improve lighting quality?
I have heard of many cons of this AO such "flickering" or something like it.

Any advice?

I turn on HBAO+ just because it looks so much better than any other AO solutions.

hbao+ in my opinion is really quite a bit better than the SSAO implementation that they use in the Witcher 3 and it runs very well on Nvidia hardware. Unfortunately it incurs about a 10-12% performance hit on my Radeon R9 280X, but despite that, I think the visual improvement is quite a bit nicer than SSAO to justify the drop in FPS.