The Fourmost cutting tools are great for balsa and thin spruce stuff . I usually lay out the stick to be cut on the plan and mark the angles with a straight edge and soft pencil . Make the cut and the final fit with the sanding block for a clean tight fit .
On the thicker spruce stuff like 1/4x1/4 or larger I use a box mitre saw or band saw to get a straight cut with less effort.
You don't need power tools but they sure do help speed up the process at times .
If you are building a design with a lot of truss structure the Fourmost tools and Zona saws are well worth the investment.