> Also, why would one choose a separate hex nut
> nozzle attached to the heater barrel rather than
> the nozzle and barrel in one?
It makes it easier to clean the barrel as you just have to take off the nut. Also you can change nozzle size, if you so please, without taking apart the entire assembly.
> Finally, what are the advantages/disadvantages in
> using the standard hex nozzle vs the bighead
> nozzle?
As far as I understand it, it takes longer to heat up, but the larger mass keeps the temperature more stable.