I have compared nutritional values in different insects. Everyone is free do a search for comparison. I have already told the OP that all insects have their ups and downs, therefore variety is important. I don't believe in a staple feeder. Some fall short in some nutrients while others have nutrients in excess. The nutritional value of some insects do not increase much regardless of what you feed and as you know, they metabolize food differently. If I recall correctly Locust are a bit high in Iron which can cause a problem if fed in excess.
A great deal comes from experience which includes:
feeding different insects
monitoring bowel movements- consistency- color- overall health
comparing nutritional content of feeders
comparing how the insects metabolize certain nutrients
There's just so much to compare and a great deal of inconclusive information, hence the reason variety is the safest route. If you are one to live on the edge and are comfortable taking risk with your geckos, who am I to judge.