In theory....yes...in practice...no. Clorox works better.

I'm trying to avoid fumes right now, so that's a good idea. Oxygen bleach needs to be fresh (stored airtight, so it hasn't absorbed any moisture) and hot to work best. At least the hottest tap temp (130), but even better to heat the water additionally.

The things is, both bleaches (chlorine and oxygen) also take time to work their best, and I don't think the thin liquid will cling to the mildew in the shower long enough to be effective. That's why thickened bleach in Clorox bleach pens are good.