Not very convenient but it is a unique experience.
Back from my trip on the junk. Great diving, with the extra day being a really good bonus for seeing more of the spectacular sea life.
It is a unique boat. The main inconvenience was the stairs to get into and out of the tender, which wasn't a problem for most. I needed help to negotiate them with the tank, but I usually need assistance with the standard 12l tank on land, as it is almost as big as I am. The crew were very helpful, so wasn't really a big problem. Convenience could be improved by availability of smaller tanks 10l or 9l for miniature divers.
The buddy system was more lax than I'm used to (I had an excellent instabuddy and we dived as a buddy pair, but there was no time allowed for buddy checks and "same ocean buddy" behaviour displayed by some others was permitted). But many divers were far more experienced than me, so it may be I'm more conservative than most in this regard.
The cabins are a bit small and the quad cabin would be really cramped with four people, but fortunately there were only two of us in the quad cabin, so it was great. Also, you don't do anything other than sleep in the cabin, so not a big deal.
Oh and the food was fantastic! Very tasty and lots of it.
Was a fun trip and good value. I have lots of video to edit.
I ended up booking to go on the Junk. Largely a combination of wanting to do six rather than four days of diving if I'm flying all the way to Thailand for it and it fitting my schedule. 20% off sale, free nitrox and alcohol (not that I'll use much) were also hard to pass by.
Going next week and keeping fingers crossed for a good experience.
Thanks very much to those who provided feedback.