The only reason its rare is because its hard to get hold of mercenary poles if your not windurstian. I personally synth one of these whenever I get the chance. Fed. Pole goes for about 15k on Leviathan. At 60 WW I can get this most of the time, its a level 20ish synth, so its easy to obtain if you have a ww friend. ;D
And I personally used this for my smn (pre-40), and farming on whm (pre-41, I like af club), its very nice. The best DD pole for awhile... I can't remember when the next one is, 40s I believe.
Also, they sell fast if you can synth them, and not many people synth them, I've never seen 2 up for stock at once personally.