A regular user can go to the configuration slicing UI via direct URL, but if they don't have access to 'Manage Jenkins' they can't see the link to it.
Seems like this is either an oversight (if they SHOULD have that ability), or a security issue (if only admins are supposed to be able to use the plugin).
If it's intended to be available to users that can edit the jobs and not just admins - consider making the config slicing link available in the main jenkins menu so that others can see it. If not, please fix the security/access checks.
Even better - integrate w/ matrix auth plugin as it's own specific permission.