I apologize for my ignorance, dear RadWindow

I use RadWindow and RadWindowManager for a while and yet I know hardly anything about them. This StackOverflow question about RadWindow in ajax scenario has initiated manifestation of my ignorance. For me it was always clear that RadWindow must be declared inside RadWindowManager and there can be only one RadWindowManager instance on a page. Perverse consequences of this combination are obvious when you use WebForms – ASPX and ASCX entanglement through RadWindow instances. ASPX must contain RadWindowManager and RadWindow that is used on the ASCX as well. What a festival of ignorance!

First of all, what is RadWindowManager useful for? I managed to find 3 reasons from the documentation:
  1. It is a convenient way how to declare property values shared among several RadWindow instances.
  2. It adds radopen, radalert, radconfirm and radprompt functions to the global window obect.
  3. Window managment API (tile, cascade, etc...).
Documentation also says that it is possible to instantiate RadWindow without manager participation. And both ways are viable: either declaratively in markup or imperatively from code behind:

var window1 = new RadWindow();
window1.NavigateUrl = "http://www.google.com";
window1.VisibleOnPageLoad = true;
window1.ID = "RadWindow1";
window1.Width = 500;
window1.Title = "Google";
window1.Height = 300;

The last line is the most important one from my perspective. Window instance is added into normal asp Panel and no manager is involved.  The window is displayed even after partial postback when the panel is ajaxified. It is due to fact that RadWindow is control like any others and it is rendered in the same way as any other controls are. The same fact is valid in the case when the window is placed within RadWindowManager. RadWindow is rendered at the same place as the RadWindowManager. In ajax scenario you have to enclose the RadWindowManager into panel that is also updated in given partial postback. It sounds weird in connection with the fact that there can be only one RadWindowManager.

Fortunately this fact is not a fact but delusion. A page could easily contain more than one manager instance. In such case radopen and similar functions always use the first manager instance.

What about performance? Other managers like RadStyleSheetManager and RadScriptManager improve Telerik-based application performance. It seems to be not true for RadWindowManager according to this site.

What is the moral of this sad story? It is not worth to be afraid to work directly with RadWindow instances. As an application does not use tons of windows it would be better to use RadWindowManager only as support for radopen & Co. functions.