I am puzzled that people seem to be suggesting that a child rescue alert is a bad idea, that is has never been used etc etc.
But way off topic.
To get back on topic - I suggest the answer to the question posed in the OP is that invoking the right to silence is significantly less risky than answering police questions.
I have struggled with this thread from the start.
Less risky to whom? Less risky to Kate? If the objective was Kate trying to protect Kate then possibly, but only possibly, the answer is yes. I say possibly because she was sitting with a competent lawyer, not in there defenceless with a bunch of policemen.
(Today's Portuguese news is about a fairly senior officer beating a father at the recent Benfica match, supposedly because dad spat at him and had taken kids plus granddad to a match that was likely to turn violent. Check the BBC news site.)
Kate had been made the lowest level of arguido possible. This gave her a lot of rights, including the right to refuse to answer questions, but perhaps more importantly, the right to see what evidence had been taken into consideration to make her an arguido. She was finally going to get the inside story on the case.
What did she achieve by exercising her right to silence?
She handed ammunition to the anti-McCanns, to be used in the hearts and mind battle, at the very time the McCanns were running a hearts and mind campaign.
On the 'no stone unturned' front, she did not do a lot to progress the search for Madeleine. Murat and Gerry did more by answering the questions.
When the twins get to the age of independent, critical thought, this is another instance that is likely to trouble them. Why did Kate leave them behind, window and patio door open, if she genuinely thought there was an abductor? Why did she not answer the questions, if she wanted to advance the search for Madeleine?
For the avoidance of doubt, I am neither pro-McCann nor anti-McCann, so please do not interpret this post along these lines.
If I had wished to progress the search for Madeleine, I would have done what Gerry did and answer the questions.