In most parts of the world “contact departure” is obsolete. Please make it optional and allow users to decide if they want to actively hand the planes over. With the option to deactivate the need the plane will contact departure on its own after passing a certain altitude which is specified in the charts.
In the UK there is always a ‘contact frequency’ message to airborne aircraft. I can see that remembering to do this is part of the ‘game’ although I don’t like the ‘on passing xxx contact departure’ message which is also not standard everywhere
The UK is special somewhat. At most airports the published freq is advisory only and expecially for the London TMA it´s “contact when in instructed”
“on passing xxx contact departure” is mainly US
In DE this depends on the airport. Smaller airports (like EDDS) usually have silent handoffs and are specified in the SID (e.g. “Contact xxx IMMEDIATELY after take-off”).
Bigger airports like EDDF, EDDM, … don’t have it and you have to handoff the A/C manually (e.g. “Contact xxx when advised by Tower”).

I would prefer a simple on/off switch in the settings to enable the option for a “silent handoff”.