The FROG trace is very intuitive, yielding essentially a musical score of the pulse, in other words, showing its instantaneous frequency vs. time. So it is generally useful to work directly with the FROG trace without the iterative algorithm.
Most people learn to read spectrograms in a few minutes.
If quantitative results are desired, however, the iterative algorithm is required. Fortunately, it is quite simple and also very reliable, even in the presence of noise. Specifically, the pulse to be measured is split into two replicas. These two replicas are crossed in a nonlinear optical medium to create a signal field, as in autocorrelation. The signal pulse is then spectrally resolved.