I know about this ink through a blog post by Nina Johansson and decided to buy one to try.
It uses pigmented ink, more specifically, ultrafine particle carbon powder is included in the ink. So be extra careful when dealing with it, especially so if you don't use your fountain pen for a long time, there's a good chance it will clog the pen. A good wash and cleaning of the nib and cartridge once in a while should keep your fountain pen safe.
Platinum Carbon Ink is rich black. In the picture above, the left belongs to Noodler's Ink and the right the Platinum Carbon Ink.
It dries fairly quickly, and is waterproof when dry.
There's a tendency for the ink to stain. It can stain the wall of your refillable cartridge. If you rely on looking at the ink level to determine when you should refill, it's not easy with the Platinum ink because your cartridge wall will be black all the way even when your ink level is low to none.
I'm not sure if I'll recommend the Platinum ink specifically. It's just another waterproof pigmented black ink. There are lots of them on the market. Another ink that I'm using is the Daler Rowney Calli Ink which performs similarly but is much cheaper. So there's not much point getting the Platinum ink over the Calli ink in this case.
It's important to note that these are all pigmented ink. You can have to clean your fountains pens often if you don't use them much. Otherwise, I'll recommend the Noodler's ink which is water-based and waterproof even though it's not pure black.
I'll update this review again in the future as I use the ink more.