I tried a variety of leather leggings recently, including: Lysse, Nordstrom brand, and Yummie, and the Spanx were the clear winner despite the fact that they were the most expensive out of all of them.  The Spanx are the most fabric-like, which might be good or bad depending on your stance.  In contrast, the Lysse, Nordstrom, and Yummie, were all very pleather-y, in that they felt exactly like how you'd expect a piece of faux-leather to feel.  The downside to them was the rustling noise made by the faux-leather swishing against itself.

The Spanx look like leather from far away, but up close they clearly are just coated fabric.  The upside is that they have far more variation to them and therefore look most like a piece of nubuck leather, especially compared to the glossy gleam of most faux-leather pants.  Personally, I think if you want your leather to look the most realistic and the least fake, it can't be glossy.  For most regular people who clearly wouldn't blow big $$ on a pair of real leather pants, your faux-leather has to be a satin matte, or else you just look like you're wearing plastic pants.  Any shine just highlights how not-real they are.  So in my book, the Spanx still win.

They're as high waisted as shown in the product image, but they don't have thick edges like Yummie or even Lysse, so you can sit down in relative comfort, and they don't roll down too much, although I'm guessing that just depends on your body type.  I usually wear a US Womens Medium in most things, but I bought a Large in the Spanx because I didn't want to visit the land of Cameltopia.  As it turns out, the Medium would probably have been fine, but I'm keeping the Large because they're pretty comfortable, and the only way to justify the insanely high price tag is to get as many wears as possible out of them, so comfort is key.

In terms of slimming power, the Spanx are pretty reliable.  Most of the slimming is in the hip area, not the thigh, but then again I ordered the Large, and could have gone with the Medium if I valued strong control over comfort.