Is collagen a good protein source?

Not as a general protein source, and this is a label fact rather than an opinion: collagen is an incomplete protein, low in some essential amino acids, so it scores near the bottom on protein-quality scales like PDCAAS and cannot substitute gram-for-gram for whey or soy toward a daily protein target. That is a statement about its amino profile, not a verdict on the specific beauty or joint claims some products make — claims we neither endorse nor evaluate here. If your goal is total protein intake, read the amino profile before paying a premium for collagen.