The Ski Man Roto Guide is an accurate true angle with ergonomic grip.
A locking system that allows you to use any file or stone and locks it in to avoid unecessary wear on the guide or tool.
These roto guides use ball bearings as the running surface against the base to allow for easy glide with less running surface than traditional guides.
The bearings also allow for a gap between the tool and the base to allow filings to drop without catching on the base.
Side edge beveling will give the skis more grip on the snow surface. Higher angles should be reserved for experienced racers; if the angle is too high the ski can "rail out" on a less experienced racer.
Higher angles are quicker to dull.
An aggressive edge (high angle - 87), may be more difficult for lighter racers (young kids or women) and may make it more difficult to recover from being up on the edge.