Splitters can still only filter out a single item type, so if your goal is to do comparisons using a single entity (for clarity reasons for instance), they won't cut it.
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Also, Factorio speedrunning has no metagame, since it's not a PvP game (well, aside from the less played PvP mode) : speedrunners don't have to adapt to changes in tactics of other speedrunners, they only have to learn new tricks that other speedrunners might discover, which is part of discovering the game itself.