I commented on this back in January, but I will again. Walking might make you feel better but honestly, it does ZERO for cardio - and if it does, you are really out of shape. Hiking hills is good. Running (not jogging) for 4 miles is good. Riding a bike, especially a mountain bike uphill, is good. Stair steppers are not even close to walking up steep hills but I suppose better than nothing. IMO riding a bike uphill is far better than a stair stepper.
I had ankle surgery in February and have not been able to run since December. I used to run four miles every other day in 34 minutes (I am 63 so slowing down a bit). Since I could not run, I either rode my road bike 20 to 30 miles every day or my mountain bike 16 miles (road bike in AZ, mountain in CO). I rode two out of every three days and hiked up steep hills on the days I didn't bike. I worked out every single day for at least one hour.
I was elk hunting last week and one morning my guide said, "we are going to walk to the top of that hill." I thought he meant the big one behind the one we actually climbed but when we topped the smaller one, he dumped his pack. I then stated I thought he meant the big hill; he replied that it was good to know I was up to the challenge. There was another hunter in camp ten years younger than me who could not walk a mile and struggled with even small hills.