PS: where in the manual does it say, that this flag is only for Comercial?

ISOMETRIC
The view uses an orthogonal projection, rather than a perspective projection. The view frustum is not a cone, but a rectangular area with a size either given by the arc parameter, or by the left, right, bottom, up border parameters . This can be used for isometric games from a bird's view perspective, or for clipping with a rectangular view volume e.g. for PSSM shaders. The distance of the camera to an object does not affect its size on the screen in this mode; this causes far objects - f.i. the sky - to appear extremely magnified. LC