Instead of steam, he slightly altered the engine's design to run on compressed air. He modified an endmill to have steeper rake and clearance angles so that it could evacuate the chips as it cut. Endmills are normally found on standard milling machines, which spin at an average of 3,000 RPMS, but his jet powered router was designed to spin at 30,000 RPMs in order to produce a clean cut with no burn marks on the wood.
This saw is so much better than the old Black and Decker that it is replacing. The base plate is solid, the blade changes are simple, the motor has plenty of power, and the saw runs very smooth with little vibration. I have noticed a slight undercut that has been mentioned on other reviews. I tried to quantify it. If I have the orbital adjustment set to its least aggressive setting and I use a fine-cut blade, making a straight cut, I have measured a 1/32" deeper cut on the bottom of a 3/4" piece of wood stock. That may not sound like much, however if you make curved cuts, this will be noticeable with cuts in the curved areas not being at 90 degree angles to the surface. I do not have experience with other high-end jig saws to know if this an expected/common behavior. Just be warned that ... full review
Consequently, they’re going to be a bit heavier than benchtop models. However, their expanding frames mean that you’ll be able to use them even in places where you don’t have access to a table or bench. This is great for construction work, or situations where you’re going to be working outside. This type tends to be a little bit bigger than the benchtop variety, and often has more rip capacity as well.