What it is, it's basically a light-colored powder product that is designed as a universal eyeshadow base. The shade is described as a yellow ivory so I don't see this working for darker-skinned girls. Even on me, and I'm definitely on the fair end of the spectrum, it's easily way too fair.
The Multi-Tasking Powders seem to be marketed not only as an eyeshadow base but also as concealer. There are at least 5 other shades to choose from and you must choose well. These are not your everyday powders. They do have a certain density and they offer plenty of coverage. Almost feels like a heavy foundation powder except it's not meant to be put all over your entire face.
To demonstrate, I've poured a tiny amount of my sample on my hand and then spread it out. It's completely opaque with so little product. Well Rested will give your lids an ivory canvas and will cover up dark spots easily.
Using it in place of my usual eye base (Laura Mercier Eye Basics in Wheat), I felt like I was putting a very opaque and clingy beige powder shadow on. Maybe I put on too much but the color is so unnatural on me that I absolutely must put on dark eyeshadow or I'll look like I doused my eyelids in rice powder. However, adding powder shadow on top of it, every color becomes sorely muted. I could limit usage to areas that require a highlighter but it looked heavy even as a highlighter. It just wasn't working for me.
You must know that this is a mineral powder. A little goes a long way. Despite claims that it's better for your skin than paraben-filled eyeshadows, it's just not my favorite. My first issue is that working with loose powders has tended to be messy for me. This one isn't so messy but I have a hard time picking up just the right amount of product. I even used BE brushes! There are faster ways to get my eye makeup done. With the Laura Mercier Eye Basics (it's a cream), I dab a little on the lid, spread out with my ring finger and I'm done with my base. I could even leave it at that. Well Rested leaves me looking fakely well-powdered and if I try to use it as under eye concealer, it settles into every fine line and emphasizes them further. Not exactly the effect I was hoping for.
Well, it was an experiment. It was a free sample and it quickly got tossed into the trash. Someone extremely fair and who prefers loose powder makeup may have better use for it.