Adjust the crampon to fit your boot before you leave the store, not the morning of your big climb. Strap-on crampons are the most versatile and can be extremely secure if the fit is tight. They can usually be attached to most any boot. The drawback is they can be difficult to adjust in wet and frozen conditions. Also, cinching them too tightly can pinch your boot and restrict circulation in your feet.
Hybrid crampons have a heel bail and toe strap.
These work great, if they fit your boots. Mountain climbers who expect to use their crampons sparingly should take a serious look at some of the new aluminum models. They are extremely light less than a pound in comparison to many standard steel models, which weigh between two and three pounds. The points on aluminum crampons may not last as long as those made of steel, especially if you spend a lot of time on the rocks, but they work great in most snow and ice conditions. And you'll definitely appreciate the weight savings after a long day on the trail.