I've just done a few plastics that I had sitting around, and it seemed to work okay without any blooming or splotchiness, even if I had a misadventure caused by not realizing exactly how quick xantham gum would bond together. I put xantham gum in the container, poured in my h2o2. Then I realized I forgot something and went to get it. I came back and had a nice mass of xantham gum sitting at the bottom.
I saw that earlier in the thread someone had picked up the 40 vol (12%) Sally h2o2 cream, I had considered using that but decided to go with the XG+Glycerin+h2o2 mixture instead. It would be certainly more convenient but I don't know if what they are using to stabilize it would have any sort of detrimental effects on the process. I also wondered if it was clear or white, because 'cream' products always make me think that they'll be white, if so, I suspect that I'd have to rely more on Oxy catalyzing and less on the UV from the light source if it had things in it that were busy reflecting all the light.
The ingredients in the creme developer (h2o2 cream) are Water (aqua) Hydrogen Peroxide, Cetyl Alcohol, Stearyl Alcohol, Isopropyl Palmitate, Lauramide DEA, Laureth-23, Laureth-4, Nonoxymol-4, Phosphoric Acid, and Trisodium Phospahte. They all seem to be surfactants or emulsifiers except for Phosphoric acid and trisodium phosphate, and neither of those look like they'd cause many problems.
I might go pick up a bottle today and see what happens unless someone notices something in the ingredients that is a big red flag.
(I finally made it through all 3 threads about this)