See his latest posted samples at Flickr:
https://www.flickr.com/photos/ned_bunnell/sets/72177720307495920/
via his DPR post here.
Whilst the photos are nice, they do lack a bit contrast and sharpness. I would expect (much) better IQ for a dedicated B&W machine, honestly speaking.
Btw, it seems that Ned does not update his blog anymore.
https://pentaxofficial.com/18527/
https://pentaxofficial.com/18482/
https://pentaxofficial.com/18512/
All in Japanese, but the pictures speak for themselves. Various Pentax original lenses were used for the tests.
https://www.yaotomi.co.jp/blog/walk/2023/04/pentaxk3iii,monochrome-kyoto,sakura.html
(in Japanese)
My impression is that while the B&W photos do have more contrasts and better tonal representation than normal digital cameras' ones, they are yet not as solid as those images produced with better B&W films, even after they are digitalised via professional-grade film scanners.
Besides, there is a side-by-side comparison against the original K-3 III, look this:
Lastly, DC Watch reports that the Ricoh has stopped to receive pre-orders of the K-3 III Mono as the tailor-made sensors have already been out-of-stock owing to the overwhelming demand. Besides, Ricoh also said that their production capacity on the Mono units was indeed rather limited.