Your hit is held when the hally is equipped at the right time or you can hold your hit by tabbing whenever the hally is 'ready'(but don't equip it if you want to cast spells first). This is useful especially when chasing a runner.That means (if I'm not mistaken) that it does not hold it's "ready" state, so when you walk up to somebody to attack them, you will be waiting until a timer is reached before an "instant" swing occurs... it sounds difficult to predict and control to me (and, again I would like to see the hard evidence against it, since that is one thing I'm pretty sure you could do in OSI T2A).
The halberd is still going to be very effective but mages won't be able to spam the hally as fast as a dexer with 100 dex. Even mages with GM resist were able to be defeated in t2a, it comes down to spell choice and spell timing. The hally was used as a finisher or at some point during spell casting, it was the choice of the mage when to use his hit. It was more strategic pvp overall because there was more choices to make in a fight.
The strategic insta-kill magic-based pvp of 1999 was more epic than the drawn-out luck-based hally spam fights w/ constant 15 mana.