You can configure the confirm dialog through a ConfirmText property that defines the confirmation text. The boolean result can be exposed in the arguments of the click event. If there is a RadWindowManager on the same page a radconfirm should be used otherwise - the browser one.

For the time being the functionality can be achieved manually as illustrated in this demo - http://demos.telerik.com/aspnet-ajax/button/examples/confirm/defaultcs.aspx

For the time being you can use the following CSS workaround:
CSS:
	<style>
		.RadButton span.rbText {
			display: inline;
		}
	</style>
ASPX:
		<telerik:RadButton ID="rbACH" runat="server" ToggleType="Radio" ButtonType="StandardButton" GroupName="test" AutoPostBack="false" Text="eCheck" Width="200px" RenderMode="Lightweight">
			<ToggleStates>
				<telerik:RadButtonToggleState Text="eCheck" PrimaryIconCssClass="rbToggleRadioChecked" />
				<telerik:RadButtonToggleState Text="eCheck" PrimaryIconCssClass="rbToggleRadio" />
			</ToggleStates>
		</telerik:RadButton>

RadButton with button type checkbox or radio has incorenct margin in Silk and Glow.

Due to the negative value of the margin, the checkbox/radio button icons are partially hidden.

The following CSS fixes the issue (for Silk skin):
    .rbCheckBox.RadButton_Silk .rbToggleCheckbox.rbIcon, .rbCheckBox.RadButton_Silk .rbToggleCheckboxChecked.rbIcon, .rbCheckBox.RadButton_Silk .rbToggleCheckboxFilled.rbIcon, .rbToggleButton.RadButton_Silk .rbToggleCheckbox.rbIcon, .rbToggleButton.RadButton_Silk .rbToggleCheckboxChecked.rbIcon, .rbToggleButton.RadButton_Silk .rbToggleCheckboxFilled.rbIcon, .rbRadioButton.RadButton_Silk .rbToggleRadio.rbIcon, .rbRadioButton.RadButton_Silk .rbToggleRadioChecked.rbIcon {
    margin: 0 !important ;

When RadButton is set as default button the client side cancel event is not working when pressing Enter key.