I don't know the level to equate it to but I think the set has great illustrative/manipulative value for algebra at any level. Once you work with it enough, you can visualize the pieces instead of needing to actually manipulate them. The set will compliment the workbooks they include or can be used with a standard textbook (with a little preparation).

My guess is that DD10 will enjoy it as will your others.

Mom to DYS-DS6 & DS3