More embarrassing than the size itself is that it is supposedly required to change the mode of the toothbrush. I truly do not think this should be allowed, but I’m not sure how to approach enforcing it.
I guess it depends on which one you have and what mode you want to change, but I have the Oral-B Pro 5000, and have been able to change cleaning modes ("Daily Clean", "Sensitive", etc) and the color of the LED at the tip without the app. The display shows a timer for cleaning time which is all the tracking I need from a toothbrush.
There could be other modes that aren't accessible from the buttons, but none that I'm aware of.
Well, challenge number one is having a consumer protection agency that's legally empowered to pull products that are defective by design from the market. Second challenge is precisely defining what is and is not allowed, but given the sheer number of stupid things that a business could conceivably do to fuck with their customers, I'm willing to give such an agency a fair amount of latitude to evaluate things and make decisions, so long as the decisions are based on a good set of core principles. (E.g., "functionality that can be implemented without a companion app must not require a companion app".)
On my IO, you can change the mode from the toothbrush, but the selection of modes to change from is on the app. However, I think it defaults to "all of them" so it's still usable without ever running the app.
There could be other modes that aren't accessible from the buttons, but none that I'm aware of.