I tried the Writing Strands as it was scheduled for My Father's World, Level 2 with 2nd Grader and Level 3 with 4th Grader. I also have the Evaluating Writing. It is okay. Black and white workbook format that encourages use of separate notebook to write in. Directions were confusing to my kids partially due to some sarcasm in it. The way the assignments are broken down feels a little strange and repetitive. I ended up modifying things and they couldn't really just read and do the assignments independently very effectively.
We switched mid year to Here to Help Learning, a video based curriculum that uses memorable humorous teaching in various locations, not just in the classroom. It has interactive components built in and my kids LOVE IT! This curriculum didn't just save writing for us, it saved school in general. My 4th grader had developed a super bad attitude towards school on an increasing number of days and this program made her want to do school again. It also gave me some sayings from Mrs. Mora (the teacher on camera) that are helpful reminders outside of writing time for my bad attitude prone child that she recognizes as quotes from Mrs. Mora and therefore receives the correction better. The projects are exciting for the kids and she walks them through the writing process very well with clear assignments and instructions for teacher and student. Writing Strands is less expensive, but the online program for Here to Help Learning gives you access to all 6 levels and a literature study for $6.99 per month for your entire family if you're okay with printing yourself and you can stream videos well with your internet speed (you can also get dvds, teacher's manual and workbook, which we opted to do because it will save us money in the long run with 4 kids and our internet isn't great).
I can't say enough good things about Here to Help Learning, if you can afford it and you want your kids to LOVE writing and learn a lot, I highly recommend it. If you want something inexpensive and no frills (and you don't mind quirky) Writing Strands could be for you.