I got a little bottle as a sample from Sephora a couple of months ago and use it every now and then. I’m about 3/4 through the small bottle.
To me, this is just glorified water. I tried this out before makeup, after makeup, both, and I didn’t see any discernible difference every time. Since then, I just use it to spray on my RT makeup sponge to dampen it before applying foundation, because it’s easier than going to the bathroom.
I found it didn’t prolong my makeup or make application smoother. As to hydration, I can’t comment on it since I don’t have dry skin. I saw literally no change whatsoever in my makeup or skin whenever I use this. I suppose while it didn’t do anything positive, it also didn’t do anything negative. Didn’t break me out, didn’t aggravate my skin, nor did it worsen my makeup in any way.
Judging by the other good reviews, it could just be that this primer water just didn’t suit my skin type (I have oily, sometimes dehydrated skin prone to acne, and though I wear an oil-controlling primer with some highlighter and bronzer every day, I only wear sheer to medium coverage foundation on the weekends). So I suppose if you have/do any of the above, I wouldn’t recommend the primer water for you.