Followup: I sent for the Piezo samples on Type 5 paper, which is nearest to the paper I normally use. A friend whose business is color management checked them out with me. I assumed we'd be duly impressed and I'd soon set up an Epson 3800 as a dedicated BW printer. But we were underwhelmed, and I remain unconvinced without seeing a different sample image.
The sample prints are very small, making it hard to observe an extended range of tonal transition. The image emphasizes the upper and lower Zones more than midtones (where I hoped to see more extension). For $43 (including postage), I was expecting something easier to evaluate.
None of the inksets seem truly neutral – all, including Neutral, are far from gray card / ColorChecker gray. The 'WarmNeutral' sample, to our eyes, is too red, and the Carbon and Selenium tonings seems extreme, like 'special effects.'
The sample prints are inconsistent, as if the profiles weren't made or used correctly. Some have considerably more shadow detail than others, which I didn't think would vary so much with the tone of the inks. Only the Carbon and Special Edition samples displayed good separation in the lower tones/Zones.
The prints don't look very good at normal light level, because one can't see into the shadows very well. You might say they have 'sub-visible' shadow detail, in the sense that they brighten up and reveal lots more shadow detail if you hold them quite near to a 5000K light source. But that's not the intensity of any light-source used in a gallery.
In viewing light of 'normal' brightness and intensity (5000K plus a tungsten source to turn off and on, looking for variation), we both preferred the prints I'm currently making with Canon 6300 (3 black inks) on Harman Warmtone Gloss Baryta +.01 Red. Some of the difference could be attributed to the small size of the samples, which keep one from seeing broad areas of tonal transition, and to the choice of an image that placed so much emphasis on the lower Zones and didn't consistently differentiate them very well. The Canon system was doing a better job of differentiating the Ansel Adams Zones II-III-IV.
As I said at the beginning, we expected to see something convincing in tonal gradation and shadow/highlight detail, but we didn't find the samples especially impressive in these respects. I wouldn't spring for the Piezo system without sending them one of my own files to print with their most neutral ink at exhibition size. If/when doing so, I'd be willing to bet – and even give modest odds – in favor of my present BW printing workflow.