I just used a HTML-Component because I wanted to use it like a label, you know, putting some fields data in it, but with the possibility to add html, like linebreaks. My problem with it is, if there are no hardcoded elements except linebreaks the control just ... vanishes from the interface. I can select it with the "outline-selector" (not sure how it is named) to see it has a size of zero pixels, I cannot make it bigger, as soon as I click on another element the control isn't clickable anymore.
How about you give it a default-size like 10x10px so it still can be selected in the radzen-designer?
PS: When you insert it first into the designer it renders in its content, but that will be gone as soon as you add a property into the content.
EDIT: Forget it, when it's just about line-breaks it's probably easier to just use some labels with display type 'block'