In some cases I have need of a button with additional options.
These options are typically put in a drop down associated to the button.

A split button makes this natural.
In this mode the user can click on the button itself or expand the dropdown and click on one of the options inside.

It would help me with my testing mostly.

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ADMIN EDIT

You may also want to vote for and follow this request for adding Id property to all components

https://feedback.telerik.com/blazor/1495842-add-id-parameter-on-all-blazor-components

If you need this attribute for testing only,  you may find interesting this request: https://feedback.telerik.com/blazor/1513117-translators-for-selenium-testing-for-the-telerik-ui-for-blazor-components. If so, Vote for it and Follow it so we can know there is interest, and so you can get status updates.

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In some cases I have need of a true/false or on/off selection.

Currently I am doing that through drop down options however it would be more natural in some cases to have a switch style button.

It lets the browser "click" the button without requiring initial focus first.

The following can be a workaround for the time being:

<TelerikButton OnClick="@OnSave" Primary="true">
    Save<span accesskey="S"></span>
</TelerikButton>

@code{
    async Task OnSave()
    {
        Console.WriteLine("saved");
    }
}