I've done the Matilda course and it was ok. It's the 2nd first aid course that I've done and was not as comprehensive as the first (which was an independent course in Australia). My husband has done a St John's course in Australia (not infant) and also found it far more comprehensive than the Matilda Infant course - but being an "infant" course, they touched on many childhood illnesses/common injuries/babyproofing your house that we didn't do in our other course.
PERSONALLY - I would rather do a full adult first aid course next time, just because I think it covers more stuff - but if you haven't done first aid before or if you specifically want to learn about childhood illnesses/how to baby proof your house etc, then an infant one is a good starting point. A good full CPR course also covers how to do CPR on infants and children as well.