I acquired the Blow Fly with a particular job in mind. That is to sand the curve on off the ellipse cut on the bench legs. There were rough marks left during the cutting phase. In the past I have used a spindle sander to remove these with good results.
This is one task however, the Blow Fly did not excel at. The cloth backed abrasive sand paper folded around the wood. This preferentially sanded the edges and not the center, resulting in a curved edge. In the above left photo how the marks are removed only on the edges. I cut the sand paper as advised on Stu's Shed to stop the paper folding in the center. This improved things but as you can see in the right photo the consistent round over is altered.
As it is so often a trusty hand tool saved the day. A vice, a rasp, and some elbow grease got things back on track. With most of the marks removed I could then used the Blow Fly not as a shaper but as a sander.
(In retrospect I would have made my initial cuts neater. Two options to improve the cutting radius of the jigsaw would be to use a shorter blade for tighter curves or remove the top section of wood with a large diameter forstner drill bit.)
What the Blow Fly sander excelled at was sanding the natural edge portions of the project. This reason alone would justify it's purchase when using natural edged wood. It had just the right amount of flexible to round over the edges in a fast and efficient manner. Some hand sanding is still required but I much prefer this to more aggressive options like a grinder. The Blow Fly mounted in a hand drill would quickly allow the edge of a natural slab table to be smoothed.
In conclusion, the Blow Fly is a well made and innovative tool. Although it didn't fulfill the purpose I had for it, what it does to do it does very well and is a welcomed asset in the wood shop.