I have had two of these things: 

https://www.mitre10.co.nz/shop/plumb-it-tap-aerator/p/289316?srsltid=AfmBOoq0kIRru8ll5Hh8sfZpH1wm9mNnSQHNZIBlckSoNHBzBopPj5dE

One worked for a while and then started leaking. 

Bought another (not realising it was under warranty) and despite multiple efforts to install it, I can't stop it leaking. 

It leaks where the metal textured ring meets the black plastic. There was an clear O ring in the packaging but no way can I get that attached with that in there. 

I feel a bit dumb, but hopefully, someone will have a quick idea.