The short handle is easier to carry concealed (ask EdWood7). In extreme CQB, the short handle will be easier to use, but I wouldn't go as short as some do.
For instance, I'd prefer the 18" RMJ Eagle Talon over most others (though I'd prefer the electrically-insulated handle on it like the Shrike has). Here's why: with the longer haft, I have the ability to get it going much faster and hit much harder (good for breaching kevlar, especially hard kevlar like a helmet) or breaching a block wall or such. In extreme CQB I have more choices as well. I can choke up to the top of the ET's handle to "make it shorter". Yes, some of the handle sticks out the bottom of my hand, but that improves balance, and if someone if coming up behind me, I have a nice, pointy piece of metal to shove in their face. The counternbalance of the weight out the end also helps the balance and enables faster movement than otherwise would be expected in a larger tool. With the hand choked up, I can make short chops (usually with the SPIKE end -- into the space between the collar bones, the head, eye socket, groin, etc), use the edge and sharp beard to hook and slice, etc. With the longer haft, I can also let the handle out in CQB to hook the enemy's knee and yank him off his feet without having to bend as far down myself.
I also have the choice of pairing it with a long knife (if you have an AR-style rifle or Mossberg 590 shotgun, the OKC35 bayonet is a dandy fighting knife). In this case, the hawk is primarily use to hook and drag the primary threat weapon of the enemy away from me, hooking arms and such to clear a path to stab with the knife, etc.
So, in short, the short haft makes it much easier to concealed carry, and has some advantages in CQB. The long haft gives you far more options, as well as being a superior tool in the woods (my non-tactical "woods hawks" range from 24-30" in length).