You can certainly choose any science you want to with RevtoRev, but oh my, I'd not want to miss "Exploration Education" along with the Inventor's Study!

Hands down, it has been my ds's all-time favorite science year. They get to build the neatest things, and it is just an explosion of ideas, creativity, and scientific reasoning when all of those awesome experiments are paired with the incredibly narrative living books in the Inventor Study! Not to mention, it has an advanced option for your older child and a standard version for your younger, so it already accounts for their different needs and skill levels beautifully.

As you prayerfully compare MFW and HOD, this past thread may be helpful...
MFW and HOD:
viewtopic.php?f=6&t=1446
HTH!
In Christ,
Julie