My $150 "smart toothbrush" (some Oral B iO model) has accelerometers to track its head position and the app lets you know if you're not covering certain areas well enough. Since using it properly (i.e. checking the app and adjusting my brushing) I don't have to go to the hygienist as often.
https://www.oralb.co.uk/en-gb/product-collections/oral-b-app for an example.
As I said it showed me I was neglecting certain areas over time and fixing that saved me more than the price of the toothbrush in under a year.
But feel free to continue to disagree with it as a gimmick. In my experience most people that do this are some of the lucky people that could brush their teeth once a week with a stick and still have no dental trouble, meanwhile a small percentage of people seem to have to take great care of their teeth, avoid a vast array of food/drink, and still end up paying out thousands each year to a dentist. Genetics plays a big part in it and you don't get to pick your genes.