I have this on my 300D, works fine. It was in the teens last week, it started and kept running on the second try(it will try three times). It will also not try if the batt voltage is too low, it has a glow plug wait period, just works pretty good. I think I'd not use it daily in the very, very cold, but now and then it's OK, and perfectly fine if the car's been run in the last six hours or so or if it's up past 30F.
Oh, and the overboost solonoid on the firewall makes a good choice for the auto start's shutoff solonoid as well. That way you can keep it all Mercedes..
