I enjoy much more flying older King Air aircraft equipped with Garmin GNS series or with the G1000. With Garmin you can very easily and intuitively fly DME arcs and holding patterns; amend, modify, change flight plans and approaches as required and as you see it
. The display of the Garmin is also much better for situational awareness.
A major draw-back of the Proline 21 is that it keeps your head DOWN while trying to operate/change/modify the FMS.
IMO Proline 21 is an over-complicated dinosaur, an over-integrated system with an obsolete logic from an earlier century.