Hagun five-hit with all that gear's possible, that's right, and by Lv.90 it'll even be possible without the use of Goading Belt (due to Store TP V, enabling you to use Velocious/Bullwhip), but I don't think many people consider what happens if you swap to physical/magic damage reduction during any of those swings: You lose the five-hit, easily (even with Keitonotachi, mind you).
There's a solution in some senses to the fact of easily losing your -hit build, which the best part of this said solution is that it doesn't even require Usukane, but it'll make you get to 100% TP .7~ seconds slower than the standard equal-haste six-hit (23%). Keep in mind, any time your six-hit becomes a seven-hit due to coming up short on TP, your duration toward 100% TP becomes a whole 5.8~ seconds slower (3.1~ seconds slower if with haste/x2march, no hasso).
Still, for the amount of times I've lost my six-hit due to physical/magic damage reduction sets, compared to the times I've kept my five-hit (every time) thus far with this new toy, I've placed a lot of trust in it.

Hidden effect: Increases your delay by 24% (turning a 450 delay weapon into 558, 437 into 541).
No, the name does not make me favor it any more than any other situational grip, even though it makes me giggle.
It also allows you to easily solo Light every Meditate, as shown here (Yukikaze>Gekko isn't shown in the SS, but I've got logs of it if you don't believe it either way):
And hey, an extra -2% physical reduction to boot too.
That aside, directly on-topic: If you're lacking a Usukane Haramaki, I wouldn't even bother with Keitonotachi, honestly, but even if you did have one, I'd still use Hagun myself, once again due to the fact of easily losing your -hit build if you swap to physical/magic reduction in the lower -hit build set, if even for one mere swing.
tl;dr: If you don't own physical/magic damage reduction sets and /NIN everywhere (and by extension can't use a polearm properly due to the lack of /WAR), by all means get a Keitonotachi and five-hit the thing.