
The disadvantage is that it is two-handed, meaning you cannot dual wield or use a shield. However dual wielding is not terribly effective until you can put skills into it, and early bucklers are fairly cost-inefficient.
While this may not seem like a huge deal, this extra 2 damage means you can occasionally one-shot early monsters, saving you time and/or money healing. The 4AC you lost can be recovered in one level, whereas two levels are required to up your damage two points.
That was pretty long but I like to explain myself thoroughly to help answer any questions!