I would persevere with the Halti if I were you, once he gets used to it, it will make walks pleasanter for both of you. Like I said, Nelly only hates hers when she thinks about it, if she's distracted by scents on her walk, she forgets that she's wearing the Halti.
Here are a couple of pics of Nelly with Dillon (sorry they're a bit big)

