I think it really depends on how much grammar you have done. I waited a while to start w/my oldest and I must say that My Mother Tongue was definitly not enough for him.
This is our second year doing Easy grammar and I love it. It is very easy to use. They are worksheets, lots of them, my kids do 2/day but I do not see how they could really learn grammar w/out the repetition.
I will probably go back to Our Mother Tongue next year…