The 21 system is a great avionics, fairly simple and user friendly.
But as normal with any equipment there are ways to make it better.
Ether from Collins or from the OEM who installs it; in my case into a Citation.
As for example:
It has an auto switch function to go from Long Range Nav to LOC (pink to green needles how FSI calls it)
Problem; nobody besides maybe the engineers you built it know when and why it is switching. And sometimes it switches on a side cone of a probably bad ILS
Or it does not switch at all. (fairly often) And to do the manual mode change while over shooting the localizer is complicated button pushing including setting the inbound CRS.
In the SIM it works 100% flawless but not in real.
Just for fun; do not touch the display reverse switch during flight. You can end up with one display only (1 from 2). It is re-settable later on the ground!
When in Vnav mode (aircraft on a 3° vertical path) and an overspeed indication occurs, it auto switches to FLC speed mode, but the pilot normally reduces power already before only for the aircraft to pitch down now to keep the speed at max FCL setting.
And in a Citation the Vne changes at around 8000’. The red tape jumps down triggering an overspeed fairly often. (when ATC high speed approved)
Gradual speed change software would make the difference.
And an auto switch back from FLC to pitch, when pitching down significantly would make it even better.
The only real bad part is related to the altitude selector knob actually the rotation speed sensitivity for alt pre select.
After years I still can not handle it ! (but might be only me)
For the training,
Use the auto switch function FMS to Loc. contrary to the said above, it makes all easier as freq. is tuned as well.
Watch the mode selector bar on the PFD display very careful; do not look at the buttons on top.
The Vnav and altitude selector functions on approach are a bit complicated, pay attention to understand FMS approach and green needle approach and the consequences for the level off at MDA.
Last word, after flying already with a vector pointers, synthetic vision and highway in the sky avionics the Collins Pro Line 21 is as conservative and simple as one can have it in a Glass cockpit.
Happy flying
Or was it Happy button pushing