Yes, they will help you do pullups.

No, they will not help you learn to do kipping pullups. Not anymore than a riding a tricycle will help you learn to ride a bike.

Warning: The worst shot I ever took to the crochital area (I feel sure this is a medical term) was administered by one of these. If you decide to try using it, you'd do well to be sure the damn thing is secured to your feet. If you stretch it 8 ft along the length of your body while your hands are above your head, your softer bits could be made to pay for slips.