do you have an SE-L? B/c that's the only 99 B14 to come with an SR20. The G20 ECU will not work on a 1.6L, only the 2.0L. Also, Auto for Auto, manual for manual, make sure the ECU works for your drivetrain.
If you do have an SR20DE (M.T, for example), you can use a G20 M.T ECU.
The advantages are: no speed limiter, raised rev limit.
Also, the 98s and 99s are somewhat different from the other cars. Us lucky 99s have to rewire the rear O2 sensor and the EGR piping in order for a g20 or pre-98 ECU to work in our cars.