A couple of months ago I received a sample vial of Blackstone Barrister Black, and have had one of my pens (a TWSBI Diamond 580) constantly inked with it ever since. I didn't know at the time that it was nano-pigement based, only that it was supposed to be permanent (and may require more frequent flushing to be safe). I've actually found it to be a very well-behaved ink - good flow, minimal clogging, fantastic waterproofness. A little slow-drying, and sometimes needs a little 'encouragement' to get started writing after a weekend layoff, but otherwise I'm really impressed.. I'll try and upload some photos of papers that I've soaked later - for now, I'm attaching a scan and a photo of my review sheet.
If you're wavering about trying this out, I'd suggest ordering a sample vial - available from JustWrite.com.au in Australia, or Anderson Pens in the US. My 30ml bottle (purchased out of my own funds) has just arrived - this'll be one of my two go-to Black inks for the foreseeable future!