It didn't tell me what to select. It did a side-by-side comparison of the various attributes of each plan, comparing things like deductibles, coinsurance, max out of pocket, etc. While I don't doubt that Gemini and its kin will offer product placement, it's a whole other thing to distort such a comparison.
I'm not saying it told you what to select in your case, I'm just saying it would be a fairly small step if Gemini's owners ever decide to do so. Of course, it wouldn't be so blunt as to say "buy this one." The summary would just use biased words when describing the prices, or exaggerate the uncertainty of the potential costs of a given plan
At first glance one might think "numbers don't lie" but I'm sure we have both seen enough advertising to know that numbers can be misused to promote one view over another, or to try and convince customers to accept a huge price hike. When the advertisers get their claws into AI, they will do this, but with misleading figures custom-generated to mislead each specific person.
To be clear, I did say I was being pessimistic. I also didn't say that in your specific case the summary was gamed to manipulate you into doing something. But since writing the original post, and this one, It is becoming clear just how straightforward it would be to subtly manipulate an AI summary to make sure that the customer chooses what the advertiser wants them to choose.
Note that Gemini is owned by Google, who make huge amounts of money from advertising. Especially personalised advertising, customised based on the huge amount of information they have about you because they have such huge penetration into web browsers, smartphone operating systems and email. I cannot imagine that they will just leave the AI advertising money on the table in the future.