Again I think this straddles somewhere between best endeavours and a fallback for things which are genuinely beyond your control. A really bad M25 accident - a once a year incident - leading to hundreds of passengers getting stuck is one thing, but not allowing enough time for a sticky day in West London is another. So I would read "beyond your control" quite tightly, and booking 2 separate flights puts you in a bad place to begin with. Where it certainly helps is under the Consumer Rights Act (see Dashboard) where the law now frowns upon unbalanced contracts. This clause was written before the CRA was extended to aviation but the previous legislation was already moving heavily against unbalanced contracts. So if BA didn't offer something like this, the law would and now does impose it anyway.

To answer your question, I think this is something that would reasonably cover totally genuinely unexpected problems, however it's always good to have insurance to cover expensive risks, if you don't want to self-insure.