Would be great to have report generated in a PDF format. It would make much better impression of a self contained report.
The benefit of having single file outweighs any pros of HTML format as this is still available through the webpage.
The disadvantages of HTML format are multiple files / folders that have to be unpacked in order to view report. Other, even more negative is inclusion of the js files, this does not create good impression in terms of internet security as there are known cases of spam emails with harmful js files attached as a part of an html document.