I ended up getting Kahtoola Nanospikes instead of Yaktrax. The construction looked better. I have used them about 4-5 times and have found them best, as
@FFigawi says, on packed snow and less effective on anything slushier/looser. I avoid ice at all costs, so can't really speak to running on that.
My microspikes are also not Yaktrax, but that is just because that's what the running store had when I wanted them the next morning.
I agree that they aren't great in slush or fluffy snow. For packed snow, a mix of snow and ice, and icy surfaces, I think they work great. But you have to keep in mind that you can only ask for so much: you should plan for your run to be an easy to moderate pace. There is some weight to them, so between that and the conditions, you'll be slower than usual anyway. I will run with them on ice, but I would definitely slow down.
I've also worn them on mixed surface where there's snow, ice, and bare pavement. It feels weird to run on them with on pavement, but otherwise it seems fine. In principle, it's probably wearing away my spikes faster, but I haven't seen a noticeable effect.
Two other comments. First, the black rubber "harness" part that wraps around your shoe to hold on the spikes definitely discolored the fabric part of my shoe. (Maybe that's just mine.) But if you like your shoes to be clean, why would you wear them in the snow and ice?
Second, it takes a lot more strength than I thought it would to stretch out the rubber from toe to heel to get the darn things on.
