Yes you maybe right on the immigration delay - I've never had to or tried to claim on it. I was more thinking of a flight delay as that wouldn't be covered by the separate carries.

Personally I just use an annual travel insurance from a provider here in Singapore for all my travel needs. I don't know the particulars of the MH insurance and I don't tend to purchase insurance through airlines so don't feel as though I can comment. Other FTers may have an opinion on hem.