My first year with a 2166 (last year) I did not use it. It came with the machine, but not installed, so I just left it out. I farm all no-till; corn, soybeans and wheat. I was very happy with the results.
For me, it is more important to have the straw spread as even as possible, not necessarily shred to bits.
The knives on my chopper are pretty wore, so I will replace them this winter.
If would suggest putting the balde assembly in it to get a finer chop on the straw. A couple times I have gotten in a hurry & forgot to push the knife assembly up when switching back from corn & there was a noticeable difference IMO. Especially if the stems are green.
You should be able to pick one up at a salvage yard but I would recomend buying the external knife adjuster kit, it will have one in it . We put one in the 2366 we use to have & it was worth every penny. Sure beats crawling up inside the combine, laying on your back & having all that crap fall in your face.