Personally I find it easier to judge glides from a curved approach rather than a straight one.
I am also teaching someone to manoeuver an a/c into a safe landing following an engine failure, not to be simply able to judge when to close the throttle to ensure you can arrive at the right point.
By fixing the position of the simultaed failure, you are able to demonstrate how different conditions and techniques affect the glide performance, this allows the student a datum to be able work out how to successfully get the machine to go where they want without power.
That is the best method I know of teaching glide judgement.
That is the most important thing, not how complex the FI percieves the manouever. Fitting in with traffic can be a problem, but it is minor compared to the benefits.