My guess is they would be just as good and reliable as the Mitsubishi Canters or ISUZUs of that size and era and likely to plug on (specially just with a snail shell on their back) until you got sick of looking at more zeros being added to the odometer.
We had the tray version of that unit as a support truck on the Peking to Paris trip. It had about 200,000km on it when I bought it in Ulaan Bataar (ex-Japanese import) and it towed a heavy trailer, often with a car on it, 14,000km on rough roads all the way to Paris without missing a beat.
Just had a look at the UK reviews and forum feedback (many more Cabstars there than here), There are many reports and the only consistent thing is rust. We do not have continuous wet weather and salt on the road.
Mechanically I found many more praising the trucks than those running them down. Lots and lots of long term operators renewing with each new generation of Cabstars for their fleet for decades.
This seems to be the general story (from a vehicle review site):
Nissan’s vehicles are known for their reliability and as the NT400 is essentially a rebadged version of the long-running Cabstar, there should be few reported problems. If buying used check for corrosion under the driver's seat - known issue
The splitter gearboxes have always been an expensive problem with little jap trucks ,ever since they started fitting them as a gimmick......both the splitters and the overdrive gears fail regularly.,and as mentioned ,any fix starts at $2500 just for parts........anyone knew a bit could probably retrofit a old Inter box,but not that easy when you are a grey nomad....Just about any jap truck box of the 70s/80s is zero parts now,with the exception of the early Toyota box,which is an exact copy of the Chev 4sp synchro,and Bedford too ,I think.