I did like how the Gae Bulg looked like an arm when he was throwing it, since Cu in myth was said to have one arm look bigger than the other when warp spasming, they even put in how it was supposed to be launched by being kicked into the target. It was more along the lines of a unblockable weapon then a unavoidable one. I guess the whole breaking thing is a take on the Gae Bulg getting stucked once it was used.
Cu if the mangaka studied up will find the Irish swords of light which Cu used Cruaidín Catutchenn, there is Cletiné which gets overshadowed by Gae Bulg, but it is a small spear which he used more often in battles until it broke, and there is the spear Del Chliss.