Kora Mercury Integrated amplifier, is it worth?

I have read great things about the sound of the Kora, and years ago, I heard one playing in a room over small monitors at the Stereophile show in NYC, and I was truly impressed with the beautiful sound. The reservation that I would have is the same that I would have with the Jadis, which is that I have heard that the bias is very difficult or impossible for the average user to access and adjust safely. Maybe other members can chime in with info on this subject.

two different classy paths to the same end, but MF or Jadis

I have a Kora Flash, which is essentially a lower power version of the Mercury and without a remote. IMHO, all of the amps you mention are great, although I personally feel that the Cary SLI-80 is not in the league of the others that you mention.

I absolutely love the Kora sound - I have owned a lot of gear and listened to even more, and somehow the Koras just seem to have a really nice balance of resolution and clarity, yet remain coherent and very musical, and just natural sounding in general. I have heard better/bigger soundstaging with other gear, but the layering/image placement and image density/image definition with the Koras are phenomenal.

On that note, my general experience with Kora (and I have had exposure to a lot of their products) is that they can be a bit fussy. The designs are unconventional. And they have nearly nonexistent US presence (currently), so if you need help and do not speak French then things become difficult very quickly.