Thanks for the update.
The EJ2 Listview Virtualization type is UI Virtualization that means when we scroll down only the content we see in the listview will be replaced, while element will stay in the DOM and will be reused for the displaying future data on scrolling. This is the basic architecture of the Virtualization in EJ2 Listview.
This type of listview can handle large amount of data and it is less DOM intensive as not much thing will be frequently manipulated in DOM like other methods. But this method comes with limitations too like others, the important factor is total height of the Listview and individual list item height, based on these values only we can predict the list item at a given scrollbar position, so it is not possible to have variable item height as we cannot determine what item to display on scrolling.
Please let us know if you have any concerns.