I heard a lot of good things about it too

Well it is marketed to be water clear I understand , non yellowing and uv resistant which are all great properties to have.

J Design Group, Modern Interior Design Firm in Miami, Florida - Contemporary Miami Interior Designers http://www.JDesignGroup.com

How did it work for you? we're seeing dark spots where kids leave soap/water on our carrera counters in the bath :(

Unfortunately I can't see the manufacturer. But I can tell you before you do anything but an excellent cleaner and do a deep clean before you put any type of sealer on any stone.
I use the Granquartz stone care system #515c
Periodic intensive cleaner. For all natural stone.
With this product you can mix it to difference strengths , depending on what your cleaning. My countertops get a 1-10 ratio of cleaner to water.
But I have used it at 1-5 for hard water spots and also at full strength on an area that was covered with a rug and has spots on my floor.

Abbyd19, I would try and use the cleaner on your water spots before doing anything else.
Google the one I just talked about.
I believe in the USA this is HMK product.