I am just going to add something really quickly. In somewhat rare cases, Ghost Shrimp have attacked and ripped up male bettas' tails. This usually happends when the Ghost Shrimp is underfed/not fed, but it will even happen with a well fed Ghost Shrimp. If you do get a Ghost Shrimp, watch your betta's tail carefully. It is a good idea to have a little bit bigger tank before you consider adding a Ghost Shrimp, as a bigger tank would decrease the risk of an attack by your betta, or by your Ghost Shrimp.
Also, one last thing. Make sure that when you get a Ghost Shrimp, make sure that it is actually a Ghost Shrimp! There is a species of shrimp that is very similar that is highly aggressive and has been reported to kill bettas. I honestly think quite afew of the stories of bettas' tails getting ripped up by Ghost Shrimp is caused by the other species looking similar to Ghost Shrimp.
FireOasis - 3g
Zachary the Halfmoon Plakat
CichlidHaven - 55g (under construction!)
0.0.7 Black Widow Tetra
1.0.1 Convict Cichlid
0.1.0 Firemouth Cichlid
HermitBase - 10g
Zephus & Monoculus the Purple Pinchers (Coenobita clypeatus)
x1 Convict Cichlid Pair (actively breeding)