I guess there is an "important" reason why Erel created B4XSet, since the difference from List seems non-existent to me.
Unless in B4i List does not exist.
1msecs vs 2msecs is either "negligible" or "twice as fast"
I suspect that it was a design decision while creating ordered lists which were needed for B4i, since in B4i order in maps is not maintained.
So when we have the mechanism of ordered list, why not add a B4XSet - it would probably take him 5 mins - no harm done and adds the 'contains' method for large sets.
The last few posts of this thread would have been a good chit chat topic.