I've been feeding grandsumo and hikari bio golds to all my FHs for a long time, and decided to order chingmix(when SP80 first came out) just to add to the staple. After about 4-5 weeks of feeding them, I noticed negative results(less feeding response, colors becoming dull, head not as full and bursting looking before, and feces was not as solid and became stringy) Getting them to accept chingmix was hard as well(chingmix is the worst tasting fish food for fish I've encountered) So I stopped using them, and after about two to three weeks, things became normal.
People who uses them swear by them. It might be because their FHs were............ juvies(obviously improving as they grow), just got them not long ago to know their look when 100%, The FHs are low grades and hence ANY slight improvement on head and pearls is very noticeable(again, this might naturally happen on your any normal pellet diet), or was being fed with inferior or less nutritious diet than Chingmix. I've had my FHs for a while(some are/were full grown), and knew when they were at their 100% in looks. When they are at their 100% with your current diet with FIXED environment without any changes but the food, and then try out the new diet for them. This will show whether that food is better, worse, or similar as the current diet you were using.
This is just my PERSONAL opinion and experience about Chingmix. I say try it out for yourself and decide. For those of you who already has been using chingmix as a staple for a long time, try other pellets to see if that improves anything. That will be a good test as well.
JP