Pros: light; complete extension of nordic stride; wide flat base for BOF control
Cons: not as versatile as 75mm binding (no telemark options)
When I say "xcountry" I specifically mean classic kick (stride) and glide skiing. From my experience; the NNNBC Magnum is the best off-trail kick and glide binding available- stable and efficient. It is perhaps the best simply because it also widely available- with a huge selection of boots to match it.
The SNS X-ADV bindings are very good as well. Though narrower than the NNNBC- the SNS X-ADV has a longer ridge on the base plate. The biggest issue I have with the SNS X-ADV is the severe lack of boot options.
On an everyday basis, I am currently using the NNNBC Magnum binding, with Alpina Alaska boots; and off-trail xcountry skis ranging from a 60mm shovel- to a109mm shovel.
My everyday skiing is over rolling terrain, with only the occasional steep climb and descent. If I had more vertical in my backyard- I would be on 75mm bindings (I still use 75mm tele bindings/boots in mountainous terrain). In conclusion; 75mm nordic/telemark bindings are much more versatile than NNNBC. But- if you do not really need the downhill control that 75mm offers- NNNBC will offer much higher efficiency and performance.
From my experience the NNNBC system is much more efficient at classic kick (stride) and glide than a 75mm binding. The fundamental concept/technique to efficient classic xcountry skiing is the "diagonal stride". Efficient classic xcountry skiing is about striding (i.e. lunging)- it is not really a "kick" that produces your forward momentum and gliding. The "kick" is really the product of pushing downwards in order to generate enough grip to lunge/stride and glide forwards on the alternate ski. Unlike 75mm bindings- the system bindings (e.g. NNNBC) pivot perfectly like a hinge at the toe; allowing complete extension of your foot as you stride and glide. Once you have experienced this freedom of movement through the stride and glide- it is hard to go back to 75mm!
Although this is technically not a telemark binding; if you mate this binding with a burly, heavy-duty boot; you would be surprised what you can do coming down a hill!
Choose this binding over the automatic binding if you plan on truly skiing off-trail. The auto bindings will ice up off-trail. The auto NNNBC bindings are fine for skiing on broken trails; such as snowmobile trails.
Choose the regular manual NNNBC binding if you are using narrow skis.