For backwards compatibility reasons Telerik Reporting supports binding directly to IEnumberable/IListSource objects (incl. arrays, collections, DataSet, DataTable, DataView, DbDataAdapter), so you can bind directly to your List. However instead you might consider using the ObjectDataSource that can handle this types of data sources.
As for the design time support, check out the following help article: Working With Data at Design Time
All the best,
the Telerik team
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