UIL2 is preferred over UIL.
It is slower than OIL (which is why OIL is the default).
But there are some circumstances where OIL
cannot be used because it requires the server
opening a port on the client (the same is true for
UIL2 is experimental because it is new.
It hasn't been used as extensively in production.
We would like people to use it, to test it.
It is clearly a better design (less synchronization).