You are right that the ASP.NET controls render less html in most of the case and they might work faster in some scenarios but the same time the built-in feature of the ASP.NET controls are far less than the provided by RadControls for ASP.NET AJAX. You need to put a lot of effort to make things work client-side with the ASP.NET controls and you get this out of the box with RadControls for ASP.NET AJAX. Client-side binding and binding to OData services is another advantage. A few more, grouping for the grid items, Excel and PDF export, scrolling for the controls displaying a lot of items and load on demand for the same, content editing as in Word on the web and so on, I cannot mention them all. And it is not only the features, but the look and feel you receive without writing a line of css.
In addition to the ASP.NET counterparts, you can find in the RadControls for ASP.NET AJAX suite a lot more components built as a result of our 10 year work and experience.
Of course it might appear that you do not need these in your current project. But if you try it, you will feel the difference and see that your development tasks are done faster.
For more information on the benefits of RadControls for ASP.NET AJAX, refer to the below pages:
the Telerik team
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