Mix climbing on granite in Norway with Ice climbing occasionally.
That means you have mostly rock while on the mixed climb? If this is the case I would advise to get a mixed blade.
What are drawbacks of using Ice blade instead of Mix blade?
Ice blades are very thin and have a conical shape. Even when they are brand-new you should most likely file them to get your blade as sharp as possible. The prior isn't necessarily true because you could have the problem to release the blade from the ice. After filing the front tip it will be extremely sharp (dot-like). Some people remove this tip so the ice tool won't enter too much. This depends on the type of ice of course. To save energy while trying to get the tool out of the ice this can be very important. That's also the reason why you shouldn't forget to file the back (top) of the blade so you can release the tool by levering away from you in the plane of swing.
Ice blades are designed to penetrate very easily and to avoid breaking the ice. Some are even B-classified because the robustness of the blade isn't the main concern. If you aren't going to abuse the ice tool by side-wise lever or torque, it will still last a long time.
Mixed or dry tooling blades are designed for rock, thus for robustness. Without taper at the top the material is thicker in general. You don't have to file them as sharp as ice climbing tools because you don't want to penetrate the rock as you penetrate ice. You place the mixed blade on small rock irregularities, often you will wedge it in cracks and therefore have high loads on the material. An ice blade will break more easily, at least it will get blunt faster. The lifespan of your blade will therefore decrease if you use the ice blade in rock especially in hard rock like granite.
Referring the answer of @ShemSeger: If you are going to push the limits and climb extremely thin cracks and hard maneuver, you are therefore able to climb very difficile/careful and you have no problem with wear (and money) you are free to use the ice blade on rock. But I think most of us won't compare ourselves with Will Gadd ;)