I tried using both methods of The HTML Editor's 'Open From Web' with
https://www.onsafelines.com/ which I guess is the site in question.
(a) 'Download only the HTML page (without images or other required files) and open it in the Editor' worked as expected, but of course appeared very differently because of the absence of the required files.
(b) 'Save to disk' with all four options ticked. That threw up the following warning:
"It appears as though this file has one or more lines that exceed 50,000 characters, and may crash the Editor if opened. It also appears to be a minified css file. It is recommended that you open the NON-minified version of this file. Do you wish to continue?"
It also said, "If your page does not display correctly or appears blank, the server may be responding slowly. To fix this, use the Open From Web function again." In fact the minified bootstrap css file did cause the Editor to hang.
I always export from SD to the local hard drive, and that seems to avoid the problem with the Editor. Since option (b) above also downloads to the hard drive, it seems no more trouble than doing so from the web.
I take the point about integration, but wonder whether in practice it's likely to be a problem.
Frank