想請教券商對客戶的保障問題 - 股票

請問一下：

1. IB的最高保障是$30 million 還是$150 million？ 如果是後者 他提到
30 million意義為何？

2. 裡面提到maximum coverage of 或 up to an additional $30 million
中的 maximum 或up 都表示[最多賠你] 萬一倒閉 客戶太多 理賠金不夠
有可能無法100％賠？

3. IB我記得會把客戶的現金和股票交給花旗等多家銀行保管
萬一倒閉了 銀行端都有客戶資料 屆時銀行直接還給客戶就好了
為何大費周章加買倫敦再保險？

不太懂這句話：

https://www1.interactivebrokers.com/en/index.php?f=2334&p=acc

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) and under Interactive Brokers
LLC's excess SIPC policy with certain underwriters at Lloyd's of London 1 for
up to an additional $30 million (with a cash sublimit of $900,000) subject to
an aggregate limit of $150 million.

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