I use the magic gear with vertical dropouts for my SS. What I have found is that anything more than about 1/8" of "stretch" [a misnomer if ever there was one] will allow the chain to drop fairly easily unless it's under load. It takes about 14 months for the chain to be unusable.

When I put the new chain on, it's fairly tight, and offers a bit of resistance to freely spinning. After a few days it's loosened up, and it's good for the next year or so with no complaints. When it's reaching the end of its life, dropping the chain will become more and more common. I might get more life out of it if my chainline was a bit better, but at ~$1/month, I won't complain.

I used to have a frame with horizontal dropouts, and got about 7-8 years out of a chain before it got to that 1/8" of stretch and skipped too much to make it usable.