I have used both mix with and without and haven't noticed much difference. Since I can no longer always find Pro Mix I use whatever mix I can get that is cheapest and is light and fluffy so it doesn't turn to brick when it dries out.

Some have said that with the moisture additives their mix stays too moist and on one thread there was a comment that it would affect germination. Don't think I had heard that before. There have been several discussion threads on this question but I could not find them using the search function.

I think it kinda depends on where you live. Here in Nevada we have very hot dry heat and the potting soil with moisture controls works just fine. If you live somewhere with lots of humidity where the containers would stay wet for longer, then it may cause problems.

I use the moisture control one when I spring sow. this way they stay a little wetter and when I transplant those moisture crystals are in the ground by the plants roots. I am not sure how much it helps tho...

Karen