The pressure is different, so it might confuse her too. I did the same thing over the summer, borrowing a Little S from a friend. I liked the control I had, but I had to constantly remind myself that any pressure I added to it would be magnified some by the hackamore rather than with my sidepull. My mare was confused by the pressure change for the first few times I used it, but figured it out pretty quick.
My mare also has a giant head, so the shank hobble wire was up against her skin. It didn't cut her, but it was definitely always putting slight pressure behind her chin.
Overall, it would a good experience that helped with stopping immediately, but eventually she decided she didn't like it as much as the sidepull so we're back in that.