I use the Initiative on Amara as my primary shield, and I only play on M10. With her green tree damage reduction, large life pool, a Stone class mod, and her elemental life steal, she can actually use the “0 shields” shields very effectively. Even when getting hit by many enemies as once, the damage reduction is strong enough to allow me to stay alive thanks to her lifesteal.
Zane can also use them well thanks to his lifesteal and Barrier, but I think right now Amara is hands down the best user of the Rough Rider and Initiative shields.