We used it. Overall it was a good program. We had the Physics one that was geared for grades 4-6th. My dd did this in 4th grade. We got the whole thing-- text, student workbook, and teacher book. The text was simple to read/understand, there was an experiment/lab for each chapter. The teacher's guide explained things further, gave answers to the review questions, and (most importantly to me) it gave me a clue as to what to expect for the lab. There were ten units. We did just one unit/month and did other science the rest of the month (random experiments, etc). A motivated kid could do the program on his/her own.
I can't remember whether it is a secular program or not. I couldn't find anything remotely religious in the physics curriculum. I imagine that the Biology one would be more of a place for creation/evolution topics.
We did think that they should have listed the age group as grades 2-6 instead of 4-6 because many younger kids would have been fine with it. You could do one unit/week if desired. If you have a particularly advanced child, you may consider going up a level. This isn't written for a "gifted" audience. We did really like it; only downside for us is that my dd doesn't like being required to read the chapter first. She also wanted things to explode and physics wasn't the place for that.