Erik Darling notes some improvements:
With the release of CTP 2.1, the problems that we saw the first time around are all gone. But there are still a couple small caveats that you should be aware of.
There’s also been a change in the way you call the function, too. You not longer need the START and STOP identifiers in the function.
There are still some limitations but it does look like the function is considerably better in CTP 2.1.