The edging tool does work for both side and base edges. It is easy to work the side edges because while working the side edge, the tool travels securely against the base material that is flush with the base edge (no risk of tipping the tool). It is equally easy to work the base edge if the side of your ski/board has sidewall material that is flush with your ski/board's edge. However, since most skis have a edge that protrudes past the sidewall of the ski, to work the base edge, you need to pay attention to make sure you are not canting the tool as you work the base edge -- it is not particularly difficult, but you do have to pay attention. Having said all that, I prefer working the base edge with a 10 or 12 inch flat file.
The tool is fixed to work at 90 degree angle -- it is not adjustable.