Have shrimps in your aquarium can be great because they provide essential nutrients for fish. Plus, adding plants around them creates an appealing balance in your tank! However, some bettas may get aggressive towards them or try to consume them, which may require segregating them immediately - it may be difficult to predict beforehand which personality your betta has though; you will only know for sure once introduced into the tank!
Good news is that providing you have the appropriate shrimp species, it should be fine to house betta fish with shrimp species such as cherry shrimp, ghost shrimp and Amanos; they tend to co-exist more easily as these varieties naturally hide from other fish and tend not to get eaten by bettas. These varieties also tend to do better if given plenty of hiding space within an aquarium environment.
These shrimps grow to large sizes that make them hard for betta fish to pick up with their mouths, providing excellent scavenging capabilities to help maintain clean waters in aquariums. You can buy these at pet stores or online, just be sure to acclimate them for at least 20 minutes in your aquarium water prior to adding them into the tank - keeping in groups of 2-4 is ideal; any less or more may cause water quality issues in the aquarium.