Poly U has it's place in modeling IMO. I use it to sheet foam wings, hinge pins, and when gluing sheeting to wing ribs and such. Remember it foam to about 4 or 5 times its size. Use the foam to you advantage and allow the expansion to fill small gaps that white glue, epoxy or CA would not bridge. Do not use it for structural parts such as landing gear areas and engine mount areas. It also is not very good for stick building. It is sandable, but harder to sand than your balsa. It also is not as strong as white glue , ca, or epoxy.
I don't use ca at all hardly, [gives me an allergic reaction] but I do use all the others.
Good luck and best wishs.