I have used two drag knives in my Shapeoko 3: the Donek D3, and the Sign Vinyl Drag Knife for CNC Machines from Widget Works. Both work great, for the right application. (And both have a 0.25 shank, so no adapters are necessary).
The Donek works best for thicker materials and simpler shapes that don’t require a lot of corner actions. I’m cutting organic shapes, and using SheetCAM with the drag knife plugin I’d get dozens of corner actions per inch, and it just didn’t work very well. (But cutting something comparatively simple, such as lettering, it works great.)
The vinyl drag knife doesn’t require corner actions, so it works much better for what I’m doing, but is limited to much thinner material, up to about .01 in my experience, whereas the D3 is supposed to cut up to .0625.
My main question about the Cricut should have been: does it work as well as the Shapeoko for cutting complex, organic shapes out of thin materials, such that I can stop switching my Shapeoko back and forth between routing and drag knifing, and just have an inexpensive, deticated machine for my drag knife work?
My site is pinecreekcarving.com if you’re wondering why I need to switch back and forth frequently…