This year both of my kids have been working out of Soaring with Spelling as a part of the overall Language Arts curriculum.
So far, I've been pleased with this curriculum for my children. I think we'll continue to use this program so long as it's successful with them both. Each lesson begins with a pretest. It's an assessment test to see if the student already knows the words being worked on this week. This is great, because my son initially had weeks that he scored 100% on the pretest, and when he did, he was allowed to skip the week, and move on to the next. My daughter however has been stressed by these initial pretests, and cries when she doesn't do well on them.
The lessons each take roughly 5-10 minutes long each day. With my daughter, I've had to add extra flash cards occasionally when words seemed slightly hard for her.
One thing that perhaps would have been helpful is a placement test. My son probably could have gone ahead a level in their program...where my daughter may have benefitted from an easier book.
Overall, I think if you're looking for a secular spelling program for your children this program is appropriate for a student who is not in need of any remediation and who is on target for their grade level.