I am not a flooring professional.  I laid my floor with a carpenter.  Personally I've never used a manual nailer, but he says it's a major back saver, which when you do the math (20-30lbs versus 4lbs of hammering pressure) makes a lot of sense.  As to tongue splitting, lower the pressure (the stapler works great with my tiny and very light senco compressor) and--does it really matter?  You can get really close to the wall, which means very little face nailing.