Top positive review
It doesn't actually track where you're brushing, but it's still a good brush.
September 23, 2016
It doesn't actually sense where you are in your mouth. With the app up, it tells you where to brush (one of 6 sections), and only senses whether you're on the inside our the outside of that section. ...That's it. And it doesn't even do that very reliably. The inside of my top left side of my mouth rarely detects properly, leaving the app to falsely report that I need to spend more time there.
The "touch up" and the "modes" that it offers tweak nothing but how long it stays on. If you buy a brush that doesn't have these features, you can mimic them by just turning the brush on again after it shuts off.
THINGS I ENDED UP LIKING
I didn't expect to want to be able to adjust the intensity. I've been an E-Series user for decades and never needed it. However, my gums started to get sore after using this new brush on high, so I switched it to medium. Now that they're healed, high is OK again. ...but it's nice to have the option.
The app poorly detecting where I'm brushing is a gimmick at best. However, after I'm done brushing, the app asks "did you floss? did you rinse? did you scrape?" It's silly, but knowing that I'd have to press the "no" button has persuaded me to floss rinse and scrape far more often than I used to. I consider that a win.
Also, the app yells at you if you move your brush too quickly–and this is by far my greatest offender. I have apparently been moving my brush far too much over the past decade, and the app is convincing me to slow it down. It's a tough habit to break, but I'm only aware of it because of this bluetooth model.
Overall, I'm pleased, and expect to get 5-10 years of brushing out of it.
UPDATE JANUARY 2017:
The "brushing too quickly" detection that I thought was so helpful now seems kind of ridiculous. The brush is vibrating at 500+ strokes per second, but me adding 3 additional strokes per second is going to leave my teeth dirty? I get that I don't HAVE to stroke with this brush, but I can't see why someone should pay extra for a bluetooth model with an app just so they can curb the habit.
I rarely use the app now. I get a notification every 2 weeks to tell me to brush with the app so that it can "sync" and track my brush life, and I do so, but the novelty of the bluetooth feature has worn off. I brush my teeth twice a day, I don't need an app to tell me that it's time to replace a head–I can just do the math. This is a solid brush and works great, but If I could do it again, I'd save my $$ and skip the bluetooth.