Fully battened:
adv; Easier to shape for the novice; drop into stack pack type cover very easily; don't flog loudly so SWIMBO is not disturbed and material last a little longer; dont flog when motorsailing; allow a little closer winded sailing.
disadv: cost; batten tension quite critical; expensive cars on big sails ( Hyde do a decent FB main with sliders for sails around 250 sq ft and it's not too expensive) take longer to put on and take off; what to do with a 4m batten when the sail is off?
Having sailed this season with a FB main I am now a convert.
Depending on your mast you might need to replace it to convert to fb. My mast groove was not compatable when I enquired prior to replacing my mainsail.
Before you talk expensive tracks and cars or replacement masts talk to Paul Austin at Hyde sails. Their FB has larger than normal sliders for standard mainsail tracks. These were a bit sticky at first till I got the tension right and added a smear of teflon grease (it white and won't stain the sails) and then the sail flies up and down.
If you fit lazy jacks the upper battens will tend to foul them as you hoist, unless you are dead into the wind. So it can take you longer to hoist the thing but there is less painfull flogging as you do it.
Although I have this problem, which doesn't bother me much, you can alleviate it by having the blocks for the lazyjacks halfway out along the crosstrees, thus widening the gap.