[maxerickson]

They are frank about also selling the data for research, it is not underhanded. It's even opt in...

For example, they talk about it on this page, which is linked from the about menu (so available with pretty small effort): https://www.23andme.com/research/

I expect lots of people also like that they get updates when information about new markers becomes available.

[sonicanatidae]

I trust them to opt me out, not at all. It's safer to just assume your data is being used, regardless, because it's free money to them. If/when they get caught selling data marked as Opted Out, they'll get a pittance fine, paid with other people's money and bonuses for making numbers that quarter.

You're welcome to trust them, but no I.