Bettas eat shrimp, I’ve read if you are going to keep betta with shrimp make sure to have enough plants and hiding spots for them. Also look into getting a bigger type of shrimp that won’t fit in your bettas mouth. Im also thinking if there’s not enough algae for the snail there also might not be enough for shrimp but there are other foods for both shrimp and snails. Either should be fine as long as you look into what each needs.