Personally, I have not used this machine. But from what I've seen and heard it appears to be useful for people who are injured or who have joint issues and want to do cardio without any impact.
I suppose if you enjoy using the machine over other forms of exercise and you're losing weight, I see no reason for you to discontinue use. However, as the poster above pointed out, you could probably get as much out of a brisk walk outside or a gym membership.
I actually have one of those! I bought it almost one year ago but it was put into storage because my husband said we didn't have room for it in our small apt.
But we have now moved into a house. I am now using it every day. But I am also walking/running in the morning for 20 minutes. I then will use the gazelle in the late afternoon or early evening for 25 minutes. I have noticed a difference in how I feel. I've been using it for 3 weeks and have lost 4 lbs so far. I feel more energetic most definitely. I like the fact that you can watch tv while using it and not worrying about it making so much noise!
Hope this helped