Wow, a whole bunch of "opinions" on what primers are/do!...
For all intents and purposes, for a regular old shooter/reloader, you won't see any difference. If you chrony your loads I'm sure you will see a difference in velocity, but I don't think it will be enough to matter much to the average guy. When I was trying to wring out the last 1/10 of an inch in accuracy for my handgun loads I kept primer loads separate (all CCI, all Wolf, all Winchester primed loads separate). I worked through a powder work up with one primer and then went to a work up with another primer, all else the same. I guess I'm not the worlds best handgun shot but I did get some pretty good loads for my Dan Wesson .44 Magnum (2" @ 50' consistently), but could tell no difference between primers/groups...