Using random rate might be okay for what you want, but you need to set the range to a range that works for you. If it's too slow, just make the range smaller (instead of 5-100, maybe 5-50) and the average rate will be much slower.
What exactly does this
effect need to do? Is it just a quick flicker on and off at a regular rate? If so, that's easy to do. Or is it more where the light is on for ~2 seconds, then flickers off and back on really quick, then maybe continues somewhat like that? Does this apply to one or more specific channels, or is this more of a global
effect that can be applied anywhere? The biggest part of building effects is being able to accurately specify exactly what you want the light(s) to do - after that, actually making the
effect is the easy part. I would consider making it an absolute
effect rather than relative
effect like you have it now, depending on what the
effect actually needs to do. Absolute effects allow you to define exactly what the fixtures should be doing, while relative effects only function relative to the
current state of the attributes of the
fixture.