I also used a brown from my NYX Cocacabana trio. It is my favorite shadow to blend out harsh lines. I've seriously used it for a month straight. If I ever get around to making a favorites video, bet that will make an appearance.
living in Puerto Rico but here, I just can't stand it. What make worse is there is no breeze. I said all that to say this...I can vouch for ELF primer. My dollar tree eyeshadow stayed on throughout the entire day. I will definitely be purchasing the ELF primer again. Bet on it.