Lots of information on this style of shooting over at The Strobist.
My biggest issue with the flash units is the lack of modelling lamp. I keep meaning to try making modelling lamps out of LED bicycle lights.
Even a light travel strobe kit is huge when you add in battery packs compared to a pair of GN120 flashes with AA batteries. The real question is "Is GN120 enough for your project?" Since I'm usually doing portraits in a small area, the answer for me (even though it goes against my GAS want for studio strobes) is yes.