For Enopi, the "Critical" part is very good for training up thinking skills. However, the "Basic" part is purely number crunching and is extremely boring.
I learnt 奧數 in secondary school and my nephew also learnt 奧數 from P.1. To me, 奧數 can train up thinking skills and students who are good at 奧數 would find the school curriculum very easy and straight forward. Having said that, the child who learns 奧數 must be very interested in Maths. Otherwise, it would be a mission impossible and he/she will lose interest and confidence in Maths at all. The child also needs to spend extra time on 奧數, since it is something beyond the school curriculum.
My son is extremely careless in doing Maths, so his school results is only around 80. He's learning Olympic Maths and find the questions very interesting. As he has to spend more time on the challenging questions, he tends to deal with the questions carefully and his performance in Olympic Maths is better than his school exam.