I laid about 25 sq m of oak flooring last year (120mm boards) and did it pretty easily without a nail gun. I just drilled (quite tight) clearance holes through the boards at 45 degrees every 200mm or so then banged the nails in and used a nail punch to lose the heads. The nailing would probably have been a bit quicker with a gun, but the time spent finding one, buying it, learning to use it, probably wrecking a few boards as I got used to it etc would certainly not have been recouped. Compared with the time spent taking the old floor covering up, measuring and cutting the boards, doing the skirting boards etc the actual nailing time was pretty trivial.
If your going to be laying loads of floors I can see the need for one, but if this is just a one off project, frankly I wouldn't bother.