I'm the ideal person to test cleansers. I do a very technical job and I often come home from work looking like this...
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I need something that's gentle to my sensitive complexion but tough on dirt.
You apply the micellar water by putting it on a cotton wool pad and wiping over the face - essentially, it's a wipe-off cleanser. I found it quite strange - it was a bit like foamy, slightly oily toner. I actually had to google the product to see if I was using it correctly, (I was).
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It's quite gentle to use in that it doesn't irritate or dry the skin and has a gorgeous fresh, floral fragrance but I didn't find it to be particularly effective as a cleanser. Although it removed all the visible dirt, the next morning when I used my usual wipe-off cleanser, I found that it lifted a lot more dirt than normal which suggests that the micellar water hadn't removed everything.
I'd imagine that if you had very sensitive skin & didn't do anything that made you get hot/sweaty/dirty, this would be the ideal cleanser but I'm not that person.
The best use I found for it was this; if I'd spent all day at home make up free and I was going out in the evening & wanted to wear make up, I'd give my face a quick wipe over with micellar water so that I wasn't applying foundation to dirty skin. However that's not enough of a reason to actually buy it.