Unless you plan to shoot bug holes with that rifle, just a few shots at a time outa the rifle, I`d FLS, and save the money for more brass. I have more than several AI`s in three different cal`s. and find that more brass is lost due to primer pocket expansion than all else.
IF you do neck size only, I would suggest the die is set up to bump the shoulder back too, if needed, and it will be needed in a few fireings, then you will have to FLS. I have two rifles in AL chamberings that will not shoot if the bolt crush fits the brass, neck sizing and not bumping the shoulder, one a 98 the other a 700. Being down the neck sizing road once or twice, I now just FLS.
YMMV..good luck
