Think lucky has one, I have an eliptical trainer.......and love using it, I did have a plain old stepper and could use it foe ages without getting a little out of breath. The eliptical trainer is good it works ur legs, arms, etc and your heart and lungs, I do get slightly out of breath too. I have managed to increase the distance too.
Good luck with whichever piece of equipment you choose.
I've got one. If you want to bend your knees you can. I'm still on crutches - 3 weeks post hip replacement operation - and can use this using the bar for partial weight-bearing. Some of the time I lean forward onto the bar and using bent knees push the peddles backwards - the angle is almost like climbing a hill but without the tension. It really makes for a cardio workout for me.