As I've said elsewhere I am a fan of EM.
IMO FWIW
Its two weaknesses are for kids who don't get things quickly -- which is obviously not an issue for your DCs. The constant movement of the curriculum is really hard for those kids. The second is that it doesn't have a lot of rote drills so some kids need reinforcement for those skills -- again it doesn't seem to be relevant for your dcs.
I like it because it is much more conceptual than most elementary school math curricula --- it encourages actual mathematical thinking rather than just learning arithmetic.
