Steve, just my opinion here but-
Pre-primed is for practice ammo only in my book. In most cases, you don't know who's primers they used, nor how they were shipped or stored before you bought them. Most likely, you'll be fine in 9,999 out of 10,000 rounds. But that 1 bothers me. And different primers do make a noticeable difference over the chrono, and on the target, if you are even half serious about it.
I've loaded hundreds of thousands of rounds in my time as a handloader/reloader. I have had exactly 1 failure in the gun. This due to a primer short it's compound that I missed in a batch of 44 magnum. The cup was obviously there, as was the anvil, just no priming compound. Since then, all of my serious use ammo is home rolled. Too many times I've had off the shelf ammo exhibit loose slugs, smashed case mouths, and either sideways or upside down primers. If I load a round like that(things do happen), it's scrapped right out of the gate. Not missed on a QC check and shipped to a customer anyway.
Not saying it's a bad idea. If you can get pre-primed for the same cost as cases+primers, it's worth it for practice ammo. Even at a small premium, I still might. Just do the math- I can prime X number of cases per hour given primers plus cases cost= Y or I can buy primed cases for Z. What's my time worth? That's a totally personal call.