[racket] Questions on Typed Racket's FlVector

Morning,

I'm putting together an equivalent of a dataframe from R in Racket.

To maximize performance of computation over vectors of real numbers is
FlVector the correct type to use in Typed Racket?
Is there some sort of performance gain by having flvector-length in
addition to vector-length?
Is the following behavior a bug?

> (vector-length (flvector 1.2 2.3))
stdin::43119: Type Checker: Expected Vector, but got FlVector in: (flvector
1.2

Thanks,

Ray
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