Consider it marked deprecated - the entire Rest-API for that matter.
We are probably still weeks (or more) from a Vault-Network that contains the new MutableData-Type but that change will happen and it will drop the current API as it is today entirely. If you take a look at our work in progress on the NodeJS-API (which will become the browser API, too), you’ll find a much smoother and easier-to-use approach. I highly recommend studying that instead.
(Docs and Tutorials, even though they only work on mocked-routing at the moment, are in the making)