The advantage of the vest is that it lets the strain or pull spread evenly over her chest and sholders and not on her neck. They can hurt themselves pulling on a collar. Their bones in their neck are fragile and can actually cause injury to themselves if they get too "fractious".
And Lordie, if there is anything Emma is, it is fractious
She weighs a big whopping 4#8oz. and is 5 months old. So sweet, likes to cuddle under mama's throw in the chair. Still likes to get up on my sholder and put her warm little belly tucked under my chin and her head on my sholder, and my heart just melts.
We graduated puppy education classes and are signed up for intermediate classes. I didn't want an unruly chi, or an anti-social one that would bite everything, so we went to class for 8 weeks. Mastered everything, but still working on the loose leash thing, now you know the reason she wears a puppia vest.
That 4# 8 oz can pull me down the sidewalk. 
