Against theft: not safe.
Most contracts only cover aggressive or break-in flights. On the other hand, no insurance that holds if a pickpocket we chip the device gently. Better to look at the exclusivity clauses ... before signing.

Maladroites: we abstain.
No refund or replacement if it falls ... "all alone". But insurance works if the breakage is due to an "outside element" like a scramble. And again ... on condition of declaring the incident within 48 hours.

That's the budget.
It takes between 5 and 20 € per month depending on the model and with the obligation to commit for 1 year. For a high-end smartphone (iPhone type), it is difficult to find a contract for less than € 9, or € 108 / year (and sometimes more). Then, the difficulty, denounced by many consumer associations, is the termination. Without registered letter 3 months and 15 days before the end of the insurance contract, it is automatically renewed for 1 year.

We take time to think.
Nothing obliges us to decide at the time of the purchase. Depending on the operator chosen, we have up to 1 month. It leaves time to read the short lines of the contract and compare it with other proposals. Such as those of their bank or their home insurance, which may have a more mobile "mobile" formula, covering, for example, loss of keys (home, vehicle) and identity papers.

Thanks to the UFC-Que Choisir.