Steve: I agree w/what PineRidge is telling you; if you are using your FEL to excavate, as opposed to just moving earth or other materials that are already piled up, there is just no comparison as to the effectiveness of the FEL w/toothbar.
I think that the physics of it is probably that all of the breakout force being exerted by the FEL is concentrated on the ends of the teeth, rather than being spread out along the entirety of the FEL blade and is, moreover, exerted onjust that portion of the earth being dug that is in contact with the teeth. This makes the cutting action of the FEL much more effective in breaking up earth and prying up rocks embedded in it.
In any case and whatever the reason, you can dig much more effectively and efficiently w/a toothbar in any kind of compacted or rocky soil.
FWIW, my toothbar fastens w/two bolt/washer/nut sets; one at each end of the bucket. It takes all of about 2-3 minutes to either remove or reinstall the toothbar.
Hope this helps.