These are both simple (when you are knocking together factory flatpack furniture) and surprisingly tricky (when you are making them, not in a factory) joints.
They were developed for factory-made flat-pack furniture, and you can bet the holes were jigged at least up until they might be CNC-ed, because the things have to line up with a great deal of precision, or they simply do not work.
The only time I've ever bought the hardware was to replace missing hardware on factory furniture. I have no dreams of competing with Ikea or the nicer, teak-ier (veneer mostly, of course) mid-century Danish factories.
I would spend some effort on making a jig that does both sets of holes (probably at 90 degrees to each other) and has means to register when clamping so that everything is as well-constrained as can be. Clamp it on the face flatways, drill the big cam holes. Clamp it to the edge of that panel, drill the holes where the bolts come to the clamps. Clamp it to the face of the other panel and drill the holes for the inserts.