The Petzl Lim'Ice ice screw sharpening device is as affective as it is simple to use. It also works on most modern ice screws, making it a very desirable product for all active ice climbers.
The device essentially works by holding your screw in a precise position so that the in-built file can effectively sharpen the teeth at the optimum angle. There are two points in which the screw is inserted, each sharpening one side of a tooth. The sharpening process is actioned via a simple slider on the side of the device, which will need to be operated around 5 times on each side of on individual tooth.
As you would imagine, the device has been developed for use with Petzl's ice screw series, however it will work pretty effectively on screws from Black Diamond, Grivel Camp etc.
When it comes to longevity, the mechanism that sharpens the screw is essentially a modified, reversible, steel file; so you can expect the device to last a similar amount of time to that of a quality standard file.