Are you just assuming there's a deceptive opt-out? They explicitly say they're GDPR compliant and will not share your info without explicit consent. It's a strong claim that they're actually lying and non-compliant, without any evidence.

My assumption, since this promo is for a few days only, is that it's like any sale; they're doing it to build their brand and attract new customers.

without reading the policy, I'd bet money there is a clause saying one or more of

1 - in the event of a sale, your data may be among the assets transfered

2 - this policy is updated from time to time and comes into effect at the time of posting, and maybe we'll notify you ahead of time

According to GDPR, in case 1 they can transfer the data to the acquiring entity only if they are GDPR compliant too, and in case 2 all data sharing must be opt-in, not opt-out, so they can’t increase the scope of sharing without notice and affirmative consent.

Doesnt that allow them to sell it for purposes _other than research purposes_?

Could they still sell it as marketing data?

Rule of PPs: The longer the document the less protection it offers.

Doesn't "explicit consent" imply opt-in?