I have found this website extremely fascinating
Loudspeakers his work is referenced a lot by people in the know.
Whilst the basic cabinet may be simpler on the surface, probably far more effort is actually required for proper design, than a regular cabinet.
Yes any one can route or jigsaw a hole in a flat board, but to make it work properly requires a massive amount of math, and there is an absolute ton of setting up to be put into practice.
When set up properly they can sound absolutely magic, but half do it and you would be better off sticking with a sealed or bass reflex cabinet.
So unlike the advice you quoted I wouldn’t suggest people try it unless they are prepared to commit to it properly, or you will wind up with the acoustic issues they mention in spades, but that is not what a proper setup sounds like.
Here’s a pic of the ball park I see the finished speakers looking like.