It looks like somebody already asked the same thing. The response was:
Yes, these are pretty much equivalent. However,
transmutecan also change the types of non-pointer types and it can also change lifetimes. You can’t do that with
as. Since transmute has such power (and therefore potential for misuse), its use is generally not recommend.
I looks like using
as can do less damage when used incorrectly which is probably a good thing.