We used one as a demo for a few weeks. Here's what we found:
-Quick connections and reduced labor costs, without a doubt.
-On runs of piping though, the pressing action seemed to pull the piping out of square, I mean really noticably out of square. This was really prominent in the larger size tubing and pipe, let's say 1-1/4" and larger.
The fitting patterns were a little longer than the "close-ruff" 90 degree elbows, so fitting allowance measurements took a little getting used to.
I don't know, maybe I just didn't use it long enough to get really good at it