Yes, they are preassembled and painted, but one could soup them up (the
hinges on top of the Kikka's wings have to go).
The advantage would be that you could get a lot of them in one fling,
rather than having to purchase them individually, so the overall price
would be lower than if you were to buy individual resin kits of them.
The main reason I sent the link was it's a fairly unique collection, and
a odd thing to find models of...particularly from Japan, who until
recently has really shied away from using the suicide weapons as subject
matter for kits.
The earliest one I remember was the Hasegawa "Ohka" that came with their
"Betty" kit sometime in the late 1970s, IIRC.
Boford products do get sold on ebay, but they don't have one of these in