It makes a good int based fighter for one, so there is that. Two the parry class feature only disallows attacks with your off-hand, it may be cheesy but natural attacks can still be taken (bite and gore are even still piercing attacks), and things like armor spikes and boot knifes still work (also piercing attacks) for TWF.
So you can still attack but forgo using your main attacks and shut down anything with 3 or less attacks. At level 5 you aren't even losing the attacks you give up. So you really just have to get creative with this Prc (Must be why it is INT based)
I was interested with the Parry ability but Seems like it suffers a bit until level 5 (and even then unless you have a way to ocasionally move while full attacking, `else you lose the benefit).
Is there a way to make this decent? Doesn't seem like this PrC is too popular.
Dervish Dance Duelist, in addition to its alliterative appeal, can tank Str into the ground, using Piranha Strike instead if desired (at level 1 before you get Dervish Dance, just shoot a crossbow or something). Both Duelist and Dervish Dance give powerful benefits to offset the fact that you are limited to a single one-handed weapon (which is enough of a drawback normally to make Duelist on its own a bit weak even with the benefits). When you add in the benefits of both Duelist and Dervish Dance, you can get some serious advantages, such as one of the best ACs in the game for a reasonably competitive damage dealer, wearing Celestial Chain for ~31 AC before counting anything but the armor bonus, Dex bonus, and Int bonus at Fighter5/Duelist5 (a normal Sword and Board Fighter10 with a +3 Full Plate and +3 Heavy Steel Shield will have ~30 before counting extras, and they tend to have the best AC).
Might as well use the archetype from APG for one-handed fighters, for that matter, though it doesn't add much.
Also a two or three level dip into monk or rogue works really nicely with the duelist. Rogue for a little extra DPS, a bundle of class skills and evasion. Monk for another source of AC, possible fast movement, maybe extra attacks with flurry and a few free feats. You only lose one BAB for the dip, as long as it's less the 5 levels.
I don't think you can make Fighter5/Duelist5 since you need BAB +6 first right?
Instead of Piranha Strike you could dip Ranger2 to grab Power Attack via Combat Style(2H).
Duelist is only 3 feats, which you get naturally. You will want Dervish Dance, so you need at least Fighter1, Rogue2*, Monk1*, or Human to get the needed bonus feat.
EDIT: Taking Rogue or Monk ranks will delay entry because of BAB.
