And I absolutely love it! I will go as far as to say that it's my Holy Grail eyeshadow primer. I still love the UDPP but I find the NARS Smudgeproof to be the more effective of the two. Both are quite similar and of thin consistency that's easily blended. NARS applies white-ish but blends out completely colourless once on the skin to matte finish. NARS is slightly more expensive than UDPP, although UDPP has more product than NARS (at 11g compared to NARS' 8g).
No longer do I worry about liner smudging across my lids and eyeshadow budging, as long as I have the NARS on I'm good to go. My liner stays perfect throughout the day and I've even been asked by a few people as to how I keep my liner in place all day even on a sweaty hot summer's day - such a lifesaver!