Hi all, just done W831 with the help of Yaktrax, have posted this on my other blog but in case you not seen it and if your thinking about getting some here are my thoughts on them:
Downsides for me were the crunching noise they made on the pavement in particular in places where there's no ice, and me checking they hadn't come off every now and then.
I wouldn't say they hampered how I ran as time and distance wise I did as I had hoped/ expected. I think after using them a couple of times I'll be more confident that they're not going to come off mid run. It does feel different with them on but not enough to put me off running, and they do give you more confidence on the road/ pavement because of the increased grip.
I tried them out on a piece of black ice outside my house before I set off by trying to deliberately to a "skid" (no puns please), don't get me wrong I think you could still slip a little but they kicked in to stop it becoming a big slip enough to have you end up on your bum. They get a thumbs up from me. Hope this helps. X