Depending on what you required, it can still be significantly faster than std::map. Any tree-based data structure is going to play havoc with cache. Also, it will perform an allocation for every single node inserted, which can become rather expensive (unless you're using some customized allocator for this).

Honestly, sorted vectors can often be a good replacement, depending on the workload, if you must have ordered data (this is what boost flat_map uses). All 3 (map, unordered_map, sorted vector) can have their uses, depending on what you are doing with the data.

If you need a better performing hash map, there's always Abseil as well.

Would you be willing to expand on that? I couldn't find any obvious well-known issues with a quick search.