There's two real differences. The security checks are done at lookup rather than when the handle is used, and they provide atomic operations and memory ordering which reflection doesn't give you. Think of them as type safe versions of some of the field access methods in sun.misc.Unsafe.
var handles also uses the polymorphic signature trick to avoid boxing/unboxing of the arguments you get with the reflection
(the same trick also allows to introduce 64 bits index array in the future BTW).
and you can also do all memory operations on arrayish values (array or ByteBuffer) even un-aligned acces.
There is an annotation that can be used in the JDK to mark methods as polymorphic. The compiler will declare the method call with the types of the arguments and result where it is called, and the VM will handle it. This allows a very small set of core methods to take variable numbers or types of arguments without boxing them or having to put them in an array.
