In the end I bought Petzl Lim'Ice and tried it with 2 ice screws - Petzl Lasersonic and Salewa UFO.
My photo is here:
http://flickr.com/gp/alpiniste/83o2hB/
I found,
1. Lim'Ice offers a fixed angle to sharpen a tooth of screw on the built-in file at a time. There are two slots for right and left-hand sides of the tooth. The bottom of the dip between two teeth is not ground by the file.
2. The fixed angle seems to be not as acute as some other screws, like DMM Revolution, that is, the teeth will get slightly shortened if you sharpen those screws. I believe the angle is set for Petzl Laser Speed. In fact, it seems less acute than even the angle of Lasersonic from Petzl itself - the teeth of Lasersonic got shortened a bit after sharpening. That means it takes a fair amount of time to reshape the teeth for your first sharpening of an ice-screw, presumably except Laser Speed.
3. The handling is actually a bit fiddly. Unless you insert the screw deep to the end, which is at times awkward and may need a bit of shaking, the tooth does not touch the file and hence is not filed.
4. The file is fairly fine. Therefore it is a significant labour to "reshape" the teeth.
5. Each tooth is sharpened one at a time. That means there is no mechanism to align the lengths of the teeth, which I understand is fairly important in sharpening ice screws. It is a user's responsibility. As mentioned above, as the handling can be a bit fiddly, you can easily lose a track which tooth has been sharpened. For that reason, to ensure the alignment of the tips of 4 teeth is not the easiest job.
6. The file can be turned over, if worn out. I guess that means you could also exchange the file with the new one, although to my best knowledge Petzl is not offering the replacement file at the moment (maybe in the future, given Lim'Ice is still brand new?).
All in all, I think it is a good tool to keep the teeth razor-sharp for the screw, whose teeth are already reasonably sharp - say, a quick job after a climbing day, providing you didn't damage your screws too badly, and providing the angles of the teeth are already aligned to the set angle of Lim'Ice.
On the other hand, it would take ages to sharpen the badly damaged teeth of an ice screw to the good standard. So, it is not ideal for that sort of use.
I hope this is some help of understanding for those who are wondering what it is like!
Masa