If by 'lash primer' you mean one of those base coats that thickens & lengthens your lashes, I say yes, they do work. Whether or not you need it, however, depends on your eyelashes. L'oreal's Double Extend waterproof mascara has a great base on one end & mascara on the other. For somebody like me with crappy lashes, I love it. It makes a huge difference in how they look & really lengthens & gives them a lot of volume. The base can be used under any mascara, actually. And the mascara itself is my all time favorite. Stays on through anything & everything. But I wouldn't spend a dime on Clinique's overpriced 'lash primer'. Their products are rubbish IMO. There are far better brands out there for that kind of price. If you're looking for something more expensive to make your eyelashes appear great without a 'primer' or a base, I'd go with Diorshow Extase mascara rather than anything Clinique sells. I was quite surprised at how great it made my eyelashes look the first time I used it, without any kind of 'primer'. Very long, more volumized & even gave my lashes a bit of a curl. I was also very surprised that it doesnt flake or run on me at all. The majority of mascaras do flake on me, which drives me crazy. Its only downfall is that its not waterproof. I'm not even sure if it comes in a waterproof formula, actually. Had I not gotten it as a freebie in one of my orders I never even would've tried it. But once this tube runs out, I'll be buying a replacement for sure. In a waterproof formula, hopefully.