There is merit in such protection. Although it's a bit rough and ready in rupturing accuracy compared to a modern circuit breaker it has no moving parts and it *will* work, eventually :) Where it falls down, a bit, is in long term minor overloads but these are quite rare events.

Were I to wire my own house again I rather think I'd put a wire fuse in series with each of the MCBs - belt and braces.

3" nail was the best Pete, bit hard to easily bend though