I was at Harbor Freight today and noticed that they have a vest that's different from the one I have, which I also bought there. I bought one and did some tests this evening. The old one was $5.99, the new one is $4.29 or so. The new one has what appears to be the good 3M reflective stuff (I'm sure it's a Chinese clone); the old one has that "glass dust melted into plastic" reflective stuff. I think the old one is the same as a lot of people here have, so I thought it would be good if people saw this.
The new one is VERY VERY much more visible at distance.

L-R: $6 HF vest, Nashbar ankle band, Jandd ankle band, $4.29 HF vest, no flash
As you can see, the new one is a closer weave while the old one is a mesh, but even the new one is quite thin and breathes a lot.

With flash

Outdoors, with flash (from 40 feet or so)

From about 120 feet away, at night with some wet snow falling, with flash, zoomed in and I cropped the picture down to just the vests. They're draped over the back of my car in the garage, that's what the stray reflectors are.
I didn't put the ankle reflectors in as I was getting wet and wanted to go back in, but the results are similar.
As you can see, the vest on the right (the cheaper one) is VERY bright, in fact more bright than the car reflectors. There's NO COMPARISON. The new one was even fairly visible in the weak "focus assist" light that my camera puts on for a second before taking the picture in low light.
Next time I get to HF I'm buying a few more and putting them in my cars and keeping some spares, in case I meet someone without reflective stuff.
I'll follow up in a few months to see if the material stands up to wear.