I would take all those things (active, growing fast etc) as a good sign, and a EBJD of 8-10cm is a rare find in a shop! I would go for it but make sure you know the pH and hardness of the water in the shop compared to your parameters at home. My EBJD is doing really well in neutral, soft-medium hardness of water and the temperature makes a real difference too - bump it up to 28ºC. He loves to eat brine shrimp and blood worm!