Hey there, well i think there is no exact right or wrong, it always depends on what you wanna do, i dont wanna say you do something wrong, its just my point of view of doing it in an other way.
Im really sorry that i have no time left, but this one i want to tell you.
A UserWidget is an abstract class, so dont try to cast something into it. It should always return null, so the casting failed. Try out with a hook from Cast Failed → new node Print String(String = “Cast failed”) or use Breakpoints to view current values of an object (rightclick on a node->add breakpoint) press play and it stop at your breakpoints location, so you can investigate f.e. NULL-references.
I want to answer your question: “Why do i need to cast this???” with another question:“Who told you to do this?” 
i will look up this tomorrow again
best regards