Indeed Steve, that is total BS written by someone who has clearly never seen a total eclipse so I think “reputable author” is rather kind. The surface brightness of the inner (K) corona is about 1 millionth of the surface brightness of the photosphere so similar to the surface brightness of the Full Moon. There is lots of very bad advice out there about looking at the totally eclipsed Sun. This is particularly awful:
https://jamanetwork.com/journals/jamaophthalmology/fullarticle/2816113
To quote: “It is not safe to view a total eclipse without added eye protection, even during the 90 seconds when an eclipse is total”. If people follow that advice on April 8 they won’t see much!
To be clear, during totality it is perfectly safe to view the eclipse with any optical aid you wish to use and no filters. I have always watched the 2nd contact diamond ring with the naked eye then switched to binoculars/telescope for totality and then gone back to naked eye as soon as the chromosphere appears just ahead of 3rd contact. For photography/video I’ve taken the filter off a minute or so before second contact and put the filter back after third contact. I have never had any sensor damage from doing that (although your experience may be different and I take no responsibility etc. etc.). My video from last April is here:
https://www.youtube.com/watch?v=QmoSTGQ6hpE
and it shows prominences and the inner corona for around a minute before and after totality.