Oral-B Pro Care 5000 Toothbrush
Although it's difficult to study, it seems that oscillating (rotating) toothbrushes are better than sonic ones. In November 2016, we got a dual pack of these guys from CostCo for $150. Prior to this, I had used a plain old toothbrush.
Much better than manual brushing
To me, my teeth suddenly had that super smooth feeling I only previously got from a dentist. My wife didn't notice such a big difference, but it seems very clear to me.
Strictly speaking, one device is more than enough for one family
We got a dual pair but found that the instructions say it takes 24 hours for a full charge, and a full charge can last 20 two-minute brushings. My very informal observations find that these general numbers seem reasonable; it does take some dozens(?) of minutes to recharge after a two-minute usage.
If you read between the lines, this means that one Oral-B 5000 can be used every 52 minutes, all day long. In other words, we really never needed to buy two. One of these things could serve 20 people a day at one 2-min. brush a day, or 10 people at two brushes a day. While it may be hit hard in the morning and evening, it still has lots of time to recover.
Before your mind leaps to "gross", you can easily buy more tips online; more on this below.
The point is that any penny-pincher does not need to buy two.
But of course, you always can... if you have two, you always have a backup if one fails. Or if someone needs to travel. Or even if you want to loan one, for somebody else to try. It's easy if you have multiple tips.
They say tips last three months, but looks to me like they last a year or more
Oral-B recommends new tips every three months (without saying how many times you brush a day). They also say they build colors into the bristles so you can see if it's aging.
But so far (six months out), our tips show really no sign of aging. So Oral-B gets 10 points for making great tips, and -1 point for trying to needlessly sell more tips.
Just wait until they start looking smooshed, like all your old toothbrushes. Then buy more tips.