I've ridden a lot of winter tires in the past 20 years. These are my daily commuters and have been for years.
What I love is
1) flat protection ( have you ever replaced a tube at 10 degrees Fahrenheit? The weight of SmartGuard is well worth avoiding that scenario )
2) Decent rolling resistance ( for a studded winter tire )
3) Good handling on most of the ice I encounter
4) Good on snow up to 2 or 3 inches, depending on the type of snow ( I ride the 40c )
4) They hold their spikes much better than most tires I've used
5) More quiet than other snow tires I've used
6) Decent handling on pavement for snow tires ( you won't be leaning hard through corners no matter what snow tire you use... but these are OK, and the benefits are well worth that sacrifice )
7) It's really awesome to be able to ride in conditions where it would be impossible or suicide with non-studded tires, and these are good at that.
Where it's limited is
1) Rutted glare ice ( stuff that's frozen smooth & solid after people have ridden walked on it ).
The Marathons are great for most of what I do, but on rutted glare ice you need something wider ( I loved my Ice Spiker pros, and am now using Dillingers on a fat bike )
2) You'll need to take a little care on lakes and ponds. You can turn, but these aren't going to do as well as Schwalbe's Ice Spiker Pros
3) Climbing is a lot more work. That's unavoidable with snow tires, and not a fault of the Schwalbes. For me the security on snow and ice, the flat protection, and the fact that the only other option is not riding at all, make the tradeoff a no brainer. And let's not forget the conditions in which turning at all is impossible without snow tires!
3) The siping on the rear wheel wears down after about a thousand miles or so, but I can't really tell if it matters.
4) When the snow gets deeper than two or three inches ( depending on the type of snow ) you'll need mountain or fat bike tires. It's not Schwalbe's fault, and its a tradeoff I'm totally OK with since these are perfect for my commuting needs. Schwalbe does make studded mountain bike and fat bike tires!
5) I don't like cornering on snow tires ( Not Schwalbe's fault ) but it's a trade-off I'm more than willing to make for the benefits & safety these tires offer.
I usually run these from December to mid-March ( Boston area ) and commute 12 miles each way. I also do mixed-surface riding ( trails in the woods and fields ) and ride an unsalted unsanded bike path as well.
When it comes time to replace these I'll be buying the same thing again, as I have for the past several ( 8 or 10 ) years.
Thank you for your feedback.