OP here. To answer your question:
I'm a beginner/intermediate. Never done either of these two, and I'm wondering whether I should learn.
If the poll is all over the place (as it is now), then I'm not necessarily inclined to spend a lot of time trying to learn something that's not really useful.
But if it was 90% "Yes, you should learn to slap & tap", then that might change my mind.
Fair enough. But the only one who decides what is useful or not is you, not anyone else.