I am using both - flexible and fixed.
I am using flexible on one of my zones and fixed on the other zones.
In both cases it skips schedules due to rain, but the concern is that the flexible schedule (and I believe the fixed one as well), skip schedules based on "there is enough water in the lawn, it is still drying out". The temperature in the last 3 days has been 95+ degrees.
In the attached image - zone 3 is on a flexible schedule, all others are fixed.