The user controls (.ascx) files in ProductsModule or any other pluggable module are actually only templates, therefore when you change the template you will also need to change the code in the control that uses this template.
When talking about sample Products module the public control ProductsView (located in Telerik.Samples.Products.WebControls namespace) inherits from ContentView control which works with repeater. If you want to create a control that will be using GridView or RadGrid you would need to create your own public control together with template. You can see how is that done by taking a look at the sample for pluggable module, which you can find here:
I hope you'll find this information helpful. Let us know if there is anything else we can do for you.
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