Depends on what you are trying to accomplish that Preview side by side with CodeView does not already do?
If you are looking for simple visual editing, then use Sigil-Ebook's PageEdit program that allows editing much like BookView did. That said, the next version of PageEdit will improve the ease of editing a number of xhtml pages in an ePub in a visual manner. So you may want to wait for the upcoming release.
See
https://www.mobileread.com/forums/sh...2&postcount=32
for a video of what is coming in the next release.
See this post which tells you about the current release.
https://www.mobileread.com/forums/sh...d.php?t=322121
Note, the new Sigil External XHtml preference setting to allow easy launching of PageEdit from within Sigil.