As an aside, I love exercise. I could watch attractive women do it for hours at a time...and there are lots of attractive women in this video.
Seriously though, I do cardio everyday for between 30-50 minutes (plus long bike rides on the weekend) and incorporate HIIT as part of my regular cardio pretty much in the same fashion as in this video (3 times a week). I don't actually rest between intervals, I just slow down to normal cardio pace.
I don't have any way of measuring my improvement except resting HR and blood pressure. My resting HR is around 60. Blood pressure normal. I just turned 70 and have been doing cardio (plus lifting) pretty steadily for 50 years.
The intensity training certainly makes me feel stronger. I wish I could measure my VO2 max.
There are places you can go to have your VO2 max analyzed. A trainer can also give you a general idea, but not as precise.