We have Spellng Power, and I like the looks of it. Starts easy and covers even my super-speller oldest child. Found this for a steal, but I'd have bought The Natural Speller if I'd found it first. It's similar in format, but I don't think it gives as many "how to teach these words" ideas as SP. (In fact, SP kind of puts it that "this is how you should do this" and not so much as suggestions. But to me, all curricula directions are suggestions on how to use the product. LOL) BUT, if your books give you key words (to make it easy) and you can spy words being misspelled in regular usage, I think that's a FANTASTIC way to teach spelling. My oldest happens to be a super speller, and we need something to continue to improve that. My youngest kiddos are just learning to read and/or recognize letters, and I like that SP has words arranged by word families and similar rules, etc. But if you can relate it to what you're doing in other subjects, I think that's great. Grats!
I bought Natural Speller which is a non-consumable book of spelling words for each grade as well as suggested activities to use with them. I liked having a guideline for what words they should be able to spell at that grade. I also use spellingcity.com.