In reply to danrock101: I have the same boots in the same size, I've climbed with Petzl Dartwin and Simond Vampire Speed.
My 2p; I'm happy with the Simond units I purchased. They have well located front points for climbing steep ice and the anti-ball plates perform as they should. I used them in Chamonix last week, see my logbook. They can be adjusted between dual/mono point. The negatives I've found; the shape of the front toe bail is asymmetric so you must tighten the heel bail fitting to ensure they don't shift on the boot. And the linking bar cannot slide into the front section of the crampon - So to store them in the bag included, you must adjust the linking bar setting. Boots any larger than 45 are unlikely to be accommodated by the standard linking bar as I have mine set to the penultimate hole.
The Dartwin's are ace, they fit the boot perfectly and climb steep ice well with minimal weight. But they do ball up A LOT and there is no off the shelf solution. Also, to replace the front points you must purchase a whole new front section.
The Simond crampons appear very similar to the Grivel equiv. but at a better price point. Also, if you pick them up from Chamonix you save shipping and import tax!
Hope this is useful.
