I have a theory on the "jumpy ID's" versus "more stable ID's at depth" within the Simplex software updates.
Some users prefer no ID to a jumpy ID at depth, while others prefer having a numerical reading to go along with what they hear, even if it's jumpy.
My Nokta Impact has a hidden setting called "Target ID Depth".
From page 11 of their manual - Target ID Depth
This setting is not present in the menu.
Adjusts the depth level that the device displays an ID for a detected target. It consists of 3
levels: Hi (High), In (Intermediate), Lo (Low). Factory default is set to ''In''.
The lower the ID depth level is, the higher the ID accuracy and vice versa. At the high level,
the IDs may become jumpy.
To change the ID depth level, pull the trigger and press the up button simultaneously. Each
time you press the up button, the ID depth level will change.
I believe they put this tech in the Simplex. Different software revisions have different target ID depth settings, but they are unchangeable on the Simplex.