this has stirred up more debate than I thought it would!
The intercom is a specific model to the helmet, you remove bits of the helmet and fit in it’s place, therefore integral.
revs1972 has it exactly as I’d see it. What I would have expected, had I knew about the zero rating of accessories at the time, would to be asked if it wanted fitting therefore saving the VAT, I would then expect to pay a reasonable amount for the fitting as then I save a little and the shop makes a little. but to offer to fit if for free and then deny the VAT saving feels a bit like they were trying it on, maybe they were, maybe they weren’t.
For example you could by a helmet and several visors along with an intercom system and pay no VAT if your interpretation is correct.
I don’t read it that way as it says fitted accessories, you can’t fit multiple visors to one helmet.