It depends which 100LG you want ? I use the 100LG with the large colour cup and I its great forthat super fine weathering andf camo.
Many people would'nt suggest this but I use the fine tip on my 100LG and I find that it is excellent for doing fine work, the only thing that is the problem as far as I know is that the paint has to be a little thinner than normal but I've found that it is worth it as I'm able to create superb mottling effects on 1/72 Lufftwaffe aircraft with ease and I've had no problems with the fine tip.
As for the sidefed airbrush, to my knowledge it is similer to a gravity fed airbrush but allows for slower spraying and better vision of the model.
Btoh gravity fed an side fed are good options for doing fine detail work with a little practice, and I would suggest either!