I made this recipe as written only omitting the pancetta. My husband and I both enjoyed it thoroughly. I found it very simple to make and did not have an issue with the sauce not getting into the shells enough as another reviewer mentioned. I did simmer the tomatoes a bit longer than 20 minutes, stirring them periodically and using a potato masher to mash them as I went. I feel as though this created a sauce of ideal consistency for the shells and recipe.
Also, in response to the reviewer who disliked the time required to prep the collards: they can be prepped quite quickly by stemming them as you would with spinach, stacking all of the stemmed leaves on top of each other and then rolling like a cigar. Cut the collards once lengthwise and then slice along the "cigar" in roughly 1" pieces. I used this method to prep the collards for this recipe and the pieces were of ideal size.