Extended Image Tracking and Spatial Track and Spatial Anchor

Hi all,

I want to place a 3D object on an Image Marker on Hololens 2. I think tracking performance should improve if I place a Spatial Anchor on image target position after tracking initialized. Because, as I understand Spatial Anchors, they trigger the Hololens to collect better spatial knowledge near to the anchor in order to keep the 3D object at the exact position (accuracy of 1cm). 

Is Vuforia maybe already using the same approach and my implementation would be redundand?

If not: Am I right that Spatial Anchor is better than Vuforia Extended Tracking?  Is Vuforia Extended Tracking using Vuforia SLAM or the Hololens Spatial Track?  

Thanks for your answer