Great Tool!
I bought one of these, a Malco HC-1, from Amazon to cut the lightening holes in the wing ribs of my RV-3B. The holes were very easy to cut, with none of the danger associated with a fly-cutter.
For these holes, it was hard to clamp them down and still get a full swing of the tool. I started with this corner clamp and one more, and later added a third and removed the corner clamp - for each rib.
Since the tool rides on a pilot, when I got near the end of the cut, I had to be sure that the tool was firmly pressed against the backing wood piece to keep it from wandering. This wasn't hard and there were simply no issues at all. All 23 cuts went real easy. Yes, the RV-3B wings are symmetric - I made a practice cut before attempting the ribs.
I used a Sioux air drill and used about 95 psi. My compressor needed to recharge five times for the drilling.
The hole was slightly rough and needed cleaning up. I used a drum sander in the drill press for that, finishing off with a Scotchbrite drum in an air die grinder. A piece of 220 grit sandpaper would have done as well, been quieter and taken considerably longer. With the air die grinder going, the air compressor was on constantly, but never dropped below 100 psi. I was running about 95 to the grinder motor.
Dave