mjlamarche--
Glad you are here asking questions! Your criteria:
1. Christ-centered - all in one - no switching from book to book to book all over the place to cover all subjects.
2. Multiple children at home (ages 5, 7, and 9, entering K, 2 and 4)
3. Easy for me and no planning work.
4. Easy to follow, not complicated, and fun for the kids to learn
As far as #1 goes, HOD is VERY Christ-centered, and the topics are usually integrated so that the Bible Study connects to the History reading. Carrie (the author of the guides) has designed the guides so that you don't need tons of different materials, especially in the younger guides. However, when it comes to reading (Emerging Readers and DITHOR) and storytime, you will obviously need multiple books! Libraries are great resources if you don't want to buy the reading books yourself.

Since all the subjects are covered in one guide for each level, your daily work is already balanced for you. You don't have to worry about taking too long for math or spelling, etc, because she has balanced the work load for each day. Plus, you can be confident that the children are doing "enough" for the day just by following the guide. This has been a HUGE relief for me since I started out homeschooling by piecing my own subjects together. I had no idea if we were doing enough each day or on track to develop certain higher level skills since I had never taught before.
For #2, HOD is very compatible with multiple children. Although, contrary to other homeschooling options out there, HOD works best when kids are placed specifically in their skill level. They work better, and it is easier to teach them. So this is not the kind of curriculum where you teach to the oldest, and the younger ones just follow along at their level. In fact, they encourage the oppposite: place the younger children correctly and add extensions for the oldest if you want to try to combine them. As far as whether or not your kids could be combined into one guide, the only way to know that is to look at the placement chart very carefully and see where they might fit. There are extensions offered for older kids to be combined with younger siblings starting with the Bigger guide. I have had my 7 and 9 yos combined until this year. I am moving one up to the next guide (Bigger) and going a bit slower with my 7yo in our current guide (Beyond). Proper placement is key for happy children!
#3. Honestly, this is one of my favorite things about HOD. Super easy for you and no day-to-day planning required. You WILL have to do the work to place your children correctly, order the guide and materials (pretty minimal), and getting the books you need for reading (if you use the library, like me!). If you buy the reading books with the rest of your materials, you're all set! I just set up a 3-ring binder notebook for my child in Bigger which took less than 20 min.
#4. This is another reason I chose HOD. It is fun for the kids to learn. I do not have the capacity or time to do the research required to add a meaningful activity or art project to our studies, but Carrie has done all that work for me! Using simple things around our house, no less. My kids love activities and art and it is such a blessing to have simple projects that completely tie in with the subjects already planned for us. It definitely helps my kids enjoy the subjects more and makes me look awesome as a mom that we have a fun project for the day. I also appreciate all the work put into the book lists for reading and storytime. One less thing for me to have to research, and the kids enjoy the books. Carrie has included everything from movement, to songs, to scribbling in sand their missed spelling words. It keeps things interesting.
This is not to say everyday is magical.

My kids and I have off days, and some subjects are harder than others for them, but learning can be hard work sometimes. I do LOVE this forum for the seasons we get stuck with bad attitudes, math difficulties, questions, etc. There are so many mommas on here doing the same thing I am everyday who have such great wisdom. It is wonderful to not feel alone in this process and have direct access to other families doing the same curriculum.
Hope that helps some!