I have never used an offset handle but I think I would prefer to have the traditional handle as the control remains where most of the axe head weight is centered. Your swing establishes the angle of impact for the bit. You control the bit by controlling the weight behind the bit when it strikes the wood. You want to keep the weight aligned behind the angle of the bit established by the swing. The tendency of the poll is to roll on an angled swing but the handle controls that if it is centered more under the poll. Also in splitting with this type of handle the handle will be more susceptible to damage being wider than the taper above it.
In general I tend to resist departure from trends established by years of men working the woods for their livelihood. They would have picked any style that was most effective to their vocation. Before departing from traditional patterns I try to understand why the patterns were developed that way. Not suggesting being stuck in a rut, just saying that before we think change is improvement we need to understand reasoning behind the original design. The curved vs. straight handles have their pros and cons. Grain runout argues for a straight handle but in this link it is obvious also that the typical single bit was known to have a somewhat curved handle.
http://naldc.nal.usda.gov/download/CAT87208315/PDF
The curved handle would give a better grip/less slippage on the bottom of the handle and does place more bit control forward without doing it at the bottom of the handle where it will be marred by being wider than the bit. The link mentions that some loggers used a curved handle on double bits which favored their primary usage side. I think the key here is not going to an extreme curve so grain runout is minimized while having some of the benefits of a curved handle for some forward control.
Just my thoughts