Bill wrote:

It outputs steering commands on DME arcs so long as
you are in GPS mode. If it's an arc to an ILS, the commands
disappear when V-LOC gets selected. If it's an arc to a vor
course, it is alive the whole time.

If one doesn't have GPSS, a regular autopilot will still do
a credible job coupling if the course pointer is kept on the
direct track heading.

Another reason to have an EHSI if it can be afforded.