Did this with my wife about 6 months ago (give or take). If you stick to lvl 1, do it until it gets boring or easy; I'd recommend pushing to lvl 2 after that.
If you're looking at just doing it for an extra few minutes to workout, then that's fine too. But, if you want to keep pushing yourself, then push it to 2 then 3.
As for results, it'd be hard to say because you're also doing another hour of cardio on top of it. I'd say you'd see results due to all the different workouts you're doing; if only lvl 1 shred, I'm not sure you'd see the results you're looking for.