I have one little tiny box shower for 7 people and I was constantly fighting mildew and soap scum. It never really had a chance to dry out good between showers. I bought an Automatic Shower Cleaner with a coupon and hung it up. It seemed to slow the build-up and times between a good scrubbing, but doesn't completely eliminate the need to clean. When I use my last refill, I am going to try filling the bottle with a vinegar/water solution. The spray seems to get most of the shower, I'm not sure how well it would do with a larger space and a shower curtain. One thing to beware of is that you have 15 seconds to get the shower door closed before it sprays. With a shower curtain, you might get spray outside of the shower, but for box style it works great. I wish it could be hung higher. You could see a faint line above where the spray didn't get. The batteries lasted a long time.
It seems really loud when my husband would use it at 5am, but we didn't notice the noise at other times of the day. We also had problems at first with the kids wanting to peek through the door and watch it not realizing it sprays out.
I have bought one in the past and just received another through BzzAgent in exchange for my review.
6 months ago