There is a reason boxers jump rope.

If you can, I would learn to do double unders...and then do a tabata of double unders. That should be a good workout.

I would consider regular jumping rope it in the same category doing intervals in running/swimming/biking, so that is how I would treat the workouts (at least, until you can do 5 mins without stopping). So while you are learning to do double unders, I would maybe just do 5-6 sets of regular jumping to a certain number so that the last 3 sets are very challenging. One or two sets won't cut it.

it's much better than nothing. It is the best cardio in terms of time efficiency, burning more calories at a given heart rate than other cardio. Unfortunately as said before this means that you'll get tired before you can do enough work to be really useful. You will improve over time, but this progress will likely be frustratingly slow.