You can't get the Umbrella (Parasol) on Disc 3 as someone alluded to; at this point in the game, 5000 points at Speed Square will earn you the Flayer.
As to the original question, I would recommend getting both, simply so you can say you have done so. It's not really all that difficult. If you absolutely can't score 5000 points, though, neither weapon will really influence how you play the game.
