I think that "beta" should be spelled "betta" and that my beta readers should become betta readers. This probably means that I'm easily amused. If I put a mirror in front of a betta reader, do they stop reading and start attacking their reflection? Perhaps they're better off as "beta" reader. Although it makes me wonder about alpha readers, and whether there are any omega readers, or anyone who are chi rho readers.
I've been fortunate in my choice of first readers. They're astute, and wonderful, and aren't afraid to tell me off. Usually with big huge red pen marks, because that's the kind of awesome they are.
Hm, probably a good thing they aren't betta readers; hard to wield red pen underwater. But still, very pretty.