Hi Gold
Got an 04 Citroen Relay SWB which is the identical van and I love it. They are made in the Fiat factory with Peugeot/Citroen mechanicals. The Fiat Ducato JTD is the same van, engine etc. (Its the later Ducato models that stopped using the Hdi and started using their own Fiat Multijet engine.)
Fuel consumption is not brilliant around the houses, but then its quite low geared and quite a big van. 22 - 28MPG is the best I get. The fuel tank holds 80 litres so filling it up will always be a shock. It's got a 7.5 cm cargo area which is bigger than the Transit of the same age.
I'm not sure about the 2006 Boxers and later, but again I haven't heard many problems apart from the back doors always leak water.
The facelift 2002 to 2006 has everything, the Hdi engine which, although not the most powerful and sporty, is fine for me. Remote central locking is a must in our business and it's standard on that model.
The only thing you need to make sure of is the internal heater matrix is a poor design and leaks water. Citroen's cure was to drain the radiator water out regularily and replace the antifreeze which seems to work in the majority of cases. It was apparently the rubber o rings that leak and a change of antifreeze rejuvinates them.
As with anything, having a genuine service history and being well cared for is an important buying consideration IMHO.
The Boxer first came out in 1994 and they were very basic. PSA mainly sold the van with the 1.9 normally aspirated diesel engine which was very slow and under powered. The 1.9TD was much faster but was very heavy on diesel when pushed (as are most turbos). Power steering was an optional extra. Gearboxes suffered badly with water damage, a problem PSA never really sorted until around 2001 and then it wasn't the best fix.
The very last models of that shape had the new Hdi engine in them with a new gearbox which is generally fine. But they lacked remote central locking and lots of those other niceties that the next model from 2002 had.
Spruce
............ and I forgot to add, Boxer also came out in a lower payload version of 660kgs (250s) instead of the standard SWB of 1145kgs, so that model's pointless in our business.