Hello,
To answer your question in the title: given the post in this forum, and with myself using KDS (V1.1.1), I can say that it is used successfully (but you were not specific in what is not working for you). The V1.1.x is matching the beta tutorials, because most things remainded the same. With the exception of the Kinetis SDK, and this depends on what you are using. See the release notes on that topic, otherwise there is a dedicated Kinetis SDK community forum (Kinetis Software Development Kit).
About your points:
Because the previous version was a beta version, there is no direct upgrade (e.g. you cannot make an in-place update). When you install V1.1.1, then this is a full/new install.
There are release notes and other documentation available on the documentation tab of Kinetis Design Studio Integrated Development |Freescale.
Importing depends on what you want to import. Importing existing KDS projects is done with File > Import > Existing projects into Workspace.
This imports eclipse projects. So if you want to import a project from mbed, then that project has to be exported as Eclipse project using GNU ARM gcc tool chain. And be assured that KDS has been tested. And that KDS is provided free of charge and community supported in this forum. And that other users including myself are monitoring it and answering questions.
I hope this helps,
Erich
