DS8 has competed in the 4-6 MOEMS through a non-school based program. The problems are interesting and definitely create scenarios where rushing and following the wrong strategy leads you down the wrong path either to fail or simply run out of time.
The best value depends on the quality of feedback and practice within the group. This year I supplemented DS' once a month club with direct problem solving instruction myself, because their discussions were more surface solution oriented than problem-solving oriented.
His grade school is going to compete this year; so, he'll be out of that group there and maybe can help his school team. He may try the middle school non-school group because the level of discussion may fit him better.