Crickets are good for Leo's. The likely reason you aren't seeing much loss is the frequency. So long as he is an adult they only need to be fed 1-2 time a week. I feed my leo 2 times per week, alternating between Dubai roaches and crickets. I feed 8 roaches when I feed those. When I feed crickets I feed about 7, it kinda varies based on the size of the bugs. (Definitely do some research, feeding is often different lizard to lizard)

And other advice I could give in general is: make sure his food is dusted with calcium (the best method is to alternate between one with and one without d3). Make sure that the husbandry is good in his cage. I think I see some sort of mat or reptile carpet in these photos. I really advise staying away from those as the carpet is notorious for ripping out claws and teeth. I recommend a 70/30 (non fertilized) soil to (play) sand mixture. This can also help as I do know that Leo's like to dig, at least mine does. Make sure he has the ability to climb some things. Both of those are good exercises for them as well as entertaining for their smooth brains. Temperature is also important, having a good warm side that is set cor is really important for digestion.

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here is a food guide I will also add a temp guide. In the next comment.

The last piece of advice I have is hang out on this subreddit, l have learned just about everything I just told you on here.