What they're referring to is that when you use tabs, you end up having some things at the end of lines have to be spaced over for alignment. Thus, you then have to turn on some way of seeing what stuff is tabs and what stuff is spaces and it turns into a big mess.
Hence why normal people indent with spaces instead of hard tabs
Epiphany is a neat little project, but my understanding is it has performance issues bc it can't use the GPU or something, like YouTube videos load slow.