Buy the Philips Sonicare 4100.

It hits every dentist checkbox the iO Series 3 does, for a tenth of the price.

What was compared

Philips Sonicare 4100 Rechargeable Electric Toothbrush, 1 Brush Head, Black | 700% More Pl... — $39.99
Oral-B iO Series 3 Limited Deep Clean Rechargeable Electric Toothbrush for Adults, Black, ... — $379.99

1. Same essentials, $340 less out of pocket
The 4100 lists at $39.99, the iO Series 3 at $379.99, a gap of nearly $340 for two brushes that both cover the dentist basics: 2-minute timer, pressure sensor, real plaque removal. That extra money buys app syncing and a travel case, not a better clean.
2. Cheaper heads keep the savings going
Sonicare replacement heads cost noticeably less than Oral-B iO heads, which are among the priciest on the market and only fit iO handles. Swap heads every three months for a few years and that running cost gap keeps stacking on top of what you already saved.
3. Quiet enough for a shared bathroom at 6am
Direct comparisons found the Sonicare 4100 noticeably quieter than the Oral-B iO Series 3. That matters every single morning if you brush before anyone else wakes up or share a thin-walled bathroom, not just once in a while.
4. Gentler on the exact spot that causes problems
Head-to-head testing found the 4100's sonic vibration marginally better at cleaning along the gumline than the iO's rotating head, and gumline buildup is exactly what dentists watch for. That is the one job a toothbrush actually has to do well.
5. Yes, Oral-B reaches back teeth better. Skip it anyway.
The iO's round head does get around back molars a touch easier, and it charges in about 3 hours against the Sonicare's much slower charge. But the 4100 only needs charging every 14 days, so that speed never comes up, and a minor reach edge is not worth $340 more.