The first product I thought of when playing with these was, of course, Hourglass' Opaque Rouge line of lipsticks. I have one and, although I like it, I probably wouldn't buy another - it's insanely expensive for quite a dry formula, and these ones from Sleek are just as good - if not better. I find that the trick with matte liquid lipsticks is to make sure your lips are 100% bare, clean and dry (but do prep with a lip balm for a few minutes if you have time), and to apply slowly, carefully and in thin layers. If I take the time to do this, I find that they last incredibly well and I am able to re-apply more on top without everything getting crumbly, messy and just generally rank.
L-R: 432 Brink Pink, 434 Party Pink, 433 Rioja Red
In terms of pigment and lasting power, these are amazing products considering they cost just shy of a tenner, and are in no way inferior to the Hourglass version. The colours are stunning - the top two are fairly neon and look better in real life, FYI - to me, these kind of strong shades look best in a matte formulation. I'm still curious about the Lime Crime Velvetines, which are a similar kind of product, but here's hoping that Sleek bring out more shades soon.
What do you make of these? Let me know if you've tried them or their Hourglass cousins!