Thats interesting, I wouldnt doubt the fact that splitting it up is better because i too believe it. But the thing is finding time i mean i usually only have about 25 minutes or so to do a HIIT session and it would be hard to find 90 minutes to do one. I think it wouldnt be something you could do everyday unless have a lot of time but occasionally.
As far as calories burnt etc, you would be burning calories in those 20 minute breaks so and for sometime after your last set so overall its probally a wider window of burning calories. So therefore more benifical, If you were to do one HIIT session of 10 minutes lets say youd only burn calories for a certain period of time (dont know roughly how long) But when your doing 3 intervals you burn in throughout all the cardio and breaks and even after your last set for however long you would with just one session.
So i think its deffinately much more benifical.