Interactive broker has extra insurance protection over the SIPC limit. How reliable is such insurance?

interactivebrokers.com - Account protection).

<Account Protection

Client securities accounts at Interactive Brokers LLC are protected by the Securities Investor Protection Corporation ("SIPC") for a maximum coverage of $500,000 (with a cash sublimit of $250,000). In addition, Interactive Brokers LLC carries an excess SIPC policy with certain underwriters at Lloyd's of London,1 which extends the per account2 coverage by an additional $30 million (with a cash sublimit of $900,000), subject to an aggregate limit of $150 million. Futures and options on futures are not covered. As with all securities firms, this coverage provides protection against failure of a broker-dealer, not against loss of market value of securities.
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