Qt3D interaction with the Quick world

Sorry couldn't find a better title for this.
Basically I want to give a feedback on the steps I am doing toward a deferred rendered scene, integrated into a QML application, with dynamic objects creation.

The reference example is this: https://github.com/mcallegari/qmlplayground/tree/master/DeferredSpotShadow

1) when moving a scene into a Scene3D element, all the meshes acquire a transparency level (looks to me like 50%), so basically you can see through them. This doesn't happen in "normal conditions" where the usual main.qml is an Entity.
You can see the rendering differences by commenting/uncommenting the main() into main.cpp on my repo

2) using javascript code to add entities to an existing scene produces two issues:
2.1) a simple CuboidMesh is rendered but it doesn't accept any property set via javascript. So it appears black and doesn't translate/rotate as requested
2.2) a Mesh entity produces an internal (non fatal) error in Qt3D:
Qt3D.Render.Jobs: virtual Qt3D::QMeshDataPtr Qt3D::MeshFunctor::operator()() Mesh is empty, nothing to load

3) can't figure out how to add an item to a ShaderDataArray.
I tried to add a spotlight to the scene using ShaderDataArray.values.append method, but I got this error:
qrc:/DynamicCreation.js:36: TypeError: Property 'append' of object [object Object] is not a function
Probably my bad here in using the right QML reference

Thanks