You are correct the Silverlight and WPF report viewers advantages are that they are native controls and that they utilize Telerik themes.
About the printing we invoke a confirmation dialog because there is a limit on the time allowed between the user initiates the dialog and when the dialog is shown. If the time limit between these actions is exceeded, an exception will occur. For more information check out the Silverlight Printing MSDN article. In your case if your customers have Adobe PDF plugin installed and OOB is not required, our suggestion is to set the ReportViewer.UseNativePrinting property to False. This way the Silverlight viewer will use it's True Print functionality that is used in the Web report viewer. Generally the True Print is faster and doesn't require additional confirmation dialog, the only down side is the dependency for Adobe or Chrome PDF plugin and that OOB is not supported.
the Telerik team
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