I think I have seen similar in the 'Educating XYZ' series, and on 'Waterloo Road' and 'Ackley Bridge', but perhaps used with more humanity than the article implies. They are just like little workspaces where pupils can't disrupt each other.
If a child is there just during lesson time, then that is a bit like it would be sitting at home revising for a day, ability to focus on work.
I think the whole point of isolation is to socially excluding them - from lessons to ensure they don't disrupt others' learning, and from break/lunch as the 'punishment'. So if a child is in isolation for say flouting uniform rules, then others won't see the rules being broken and the pupil 'getting away with it'. Or is a pupil has hurt another, it keeps them away as a breathing/calming down space.
I think work would be sent down by relevant teachers, they wouldn't be twiddling their thumbs all day.
So I suspect the issue is how the school is using them, not the fact they exist.
Teachers - feel free to contradict my understanding!