I use them and LOVE them! it's a multi-functional
harness in that it can be used to teach your dog not to pull, or flipped around so it clips on the back and allows them to pull. You can also have it replaced through the company for only $8! So I think it's well worth the investment
As for teaching her to walk on a loose leash- tire her out first. If she has already been zooming like crazy around the yard with you, she'll have less of an urge to drag you down the road. You didn't say how old she is- but once she's old enough, you can actually teach her to pull- and then teach her not to pull. It's like teaching a barky-dog "speak" and then "quiet"
Good luck!