Queens59,
The Dartington is a good hive. It most certainly has it's down-sides. I would not want all my colonies in them. I certainly don't want any more at this present time (I have 2 Dartingtons and a beehaus).
There is little, other than a huge price difference, between a wooden Dartington and a plastic beehaus - I would go for the Dartington every time, but I made my own and was able to do that easily and accurately; others may not be able to follow that course.
Graham White (linked on the OMF threads going at the moment) said his Dartington out-performed his Nationals (14 x 12s, IIRC). I don't count jars of honey per hive as I consider it a waste of my time (irrelevant when one boosts one colony at the expense of another), but I do like the over-wintering plusses. Maybe it was because it performs better in the colder climate of central/north Scotland.
Swarm control is easy, but then, I find it easy enough on Nationals.
I think you need to examine one at close quarters and get a feel for the operation, if you can find one near to you. I don't like the half supers and most get used elsewhere for other duties, but for someone with a lifting difficulty, they may make life so much easier. Even so, there are ways around that problem....
Again, every hive has it's plusses and it's minuses. It comes down to a personal choice in the end - usually after trying it. I would persevere with the WBC if you can. They, too, are a good hive. Only when you understand all the gremlins in that design should you be considering change.
Everything is actually going to be heavier than an original WBC - if only by the extra frame in the box, although WBC boxes can be of lighter construction by virtue of not needing to be so weather-proof. WBCs will swarm sooner if the laying area is restrictive, so brood and a half is usually the minimum these days. 'Double brood is better' will be the response from most.
So never an easy choice. It has taken me ten years to go through WBCs and standard Nationals, to 14 x 12s, to OMFs, to top bee space, to add Dartingtons and now the dreaded plastic Dartington. I am lucky; I can cope, convert and build myself. Take your time in any decision making.
Regards, RAB