So I took O.P.I Do you lilac it? and Eyeko Lilac nail polishes and did a bit of a quick comparison.
They look identical in the bottle. Take a look at these photos of the process!


Two coats + top coat
Eyeko is less shiny but doesn't snag as easily. 

It's not news to us that with most things in life, you get what you pay for. O.P.I nail polishes retail for ~£10 and Eyeko for ~£3. I was impressed with the Eyeko but if I reach for a lilac again, it will be the O.P.I.
Who knows, Eyeko might bring out a colour that isn't in the O.P.I range!
I feel like I am wearing odd socks, as one hand is Eyeko, the other O.P.I.