That little buzz feels like a click on my Air's trackpad and like a tap on my iPhone's keyboard. Any other vibration thingy I came across feels like a vibration thingy, not like a click, not a tap.

As nobody else seems to care or is able to build the same, maybe it is worth a dollar or two. Though 5.7B is a bit much.

A dollar or two? Per device that infringes?

Apple has sold over 3 billion iPhones and 4.5 billion iPhones, iPads, and iPods together.

$5.7B seems low if every one of those devices infringes.

If it’s iPhone 6s and later and all watches (for taptic input), that’s around 2 1/3 billion phones and 1/3 billion watches, so even just $2/device gets you into that range.