I've tried virtually all such products on the market and even made my own (during supply shortages) and this is by far the best I've used (for over 20yrs). Works on porcelain (tub, tiles), plastics (shower head, PVC, plastic shower stalls), glass, shower curtains (plastic, vinyl, peva), metal fixtures (knobs) to keep soap residue, hard water issues at bay (often preventing it altogether for months) and prevents the growth of molds and mildews (even keeps existing patches from spreading).... It is harmless to sealants (silicon used around tubs, etc.), finishes and grout. There is no overpowering odor and no slippery residue that refuses to rinse off --- I usually run the shower a few seconds to get the hot water going and that time is enough to cleanly rinse away the shower spray from previous use, leaving the bottom of the porcelain tub squeaky clean.A must have for those with glass shower doors who're constantly battling mold in/on the tracks and other nooks-&-crannies where water always seems to sit.... Spray the tracks after every shower and you'll never have to deal with unsightly mold/mildew again. That said, this product isn't intended to be a killer of existing mold/mildew, but, rather, an exceptionally effective preventative of it.... Start with a clean mold/mildew free surface and this spray will keep mold/mildew from growing with regular use (after every shower or after the last person in line finishes with the shower).Excellent product! Its effectiveness is best when used daily and when spray directly on the wet surfaces (don't wipe down or squeegee the area first). In my case, it has cut down the need to scrub down the tube/shower area to once a month (could actually go longer, but I choose not to). Greatly extends the life of shower heads -- keeps them from clogging with mold & mildew growth and mineral buildup.One note to be made..... If you have brass fixtures, particularly ones that are old, this product will tarnish them. Spray them down with a product like Lime-Away at cleaning time, though, and they'll be nice and shiny again. It takes about 1-2wks to tarnish brass to where it needs to be cleaned up, but it's not actually damaging anything since Lime-Away cleans up the tarnish without any scrubbing. Just something to note is all.... It's the only metal that I've noticed to be effected in any negative way by this product, but it is noteworthy as some folks like brass knobs 'n' things. Doesn't effect shower heads in my experience (unless brass).