I think most of Anna's workouts are labelled HIIT, but she has both high and low impact sessions, with and without weights. I often do them at my own pace, depending on how energetic I feel. Her back catalogue is huge, so I always manage to find something.
As for the Bowflex 3-minute plank, I cannot recommend it highly enough. I'm really not superfit, especially after not having been able to work out regularly for the past 6-8 months, but my core is still solid. Do it every day for a month and you won't believe the difference!
Especially if you combine it with Rebecca Louise's Best Abs. (But do remember to turn the sound right down after you've done it once...)