I have heard VT and HM's can be slower because of their tails and I have also heard that shrimp fair better if there is alot of moss and carpet like plants so they can hide from the betta. I would like to try shrimp but I think they would become snacks plus the only ones I ever see here are the much bigger bamboo shrimp and one of them is like $12.
Two years ago I had a crowntail that left my shrimp alone, he's my avatar picture. I wish my baby betta was as docile as he was. I would try if he eats ghost shrimp, they are like 10 for $1 dollar