Regarding the “Neon Tetra”: The difficulty level was just right for a six year old. The pre-drilled holes were great. On Saturday we were waist deep in the pool. It passed the float test with flying colors, looking very sub like. The fun started when we wound it up. I confess I had doubts about the torque from the prop but it dove under the surface, traveled across the bottom and did a very realistic climb to the surface. All that to the total amazement of an extremely thrilled 6 year old. It is a great kit and made for a fun weekend.