Basic testing worked just fine. The unit powered up, the morse information display appeared to be working and satisfying relay clunks were heard when putting the unit into and out of bypass mode.
After sorting out some appropriate cables I tested the unit with my FT-817ND in the backyard with a 7 metre squid pole and a couple of counterpoise wires. I tested 80-10 metres successfully!
Tuning took a few seconds of relay clattering to accomplish but SWR was fine at both band ends and band-middle for each band.
I purchased the optional FT-817 control cable. This appeared not to work, but I suspect that is because it has made some assumption about the CAT data rate and I've modified it. I'll sort that out next.