The pigtails are available in solid or stranded, each prestripped on the ends. I used plugtails on a small project at the university over the summer due to scheduling on an extremely tight timeline. I only installed 25 or so so I can't provide data on labor savings. The way they were useful to me was I was able to move that chunk of labor from trimout to rough. Since rush jobs only get worse closer to the end, it was worth it in this case.
Here's what I paid for the parts:
6" plugtail, solid or stranded, $1.14 each
Extra heavy duty 20A duplex, $10.96 each
Decorator duplex, 15A, $6.62 each
GFCI duplex, 20A, "spec grade" $15.87 each
For comparison, commercial spec grade side wire recep, #CS20, $2.10 each
I should mention that the bill was just paid and not many questions asked as long as we made the deadline:grin:.