All Dash 8s have very redundant electrical systems which allow loss of any 2 out 4 generators with all electrical capability remaining. I always found that reassuring and almost as good as the -7 where you had 4 generators each
Also all the Dashes have more or less fully dual redundant flight controls with alternate cable runs for 1/2 elevator and ailerons/spoilers. How do the ATRs compare on that?
As for controly harmony, the -8-100 and -8-300 are quite nice while the -400 has oversensitive power levers and a rather "stiff" feel in the ailerons.
One big drawback about the -400 is that deHavilland didn't use a lot of the potential contemporary avionics technology would offer in order to keep it as close as possible to the -100/-300. The flight warning system with almost no concept of priority and no inhibition of minor alerts during critical phases of flight is definitely outdated. The Fokker 50 was better on that 20 years ago.
Does the ATR have some kind of thrust rating/automatic power setting system? The -400 has it and it works nicely but the -300 requires constant checking and re-setting of torque up to top of climb.
As for ratings, the -300 and -400 can be flown with alternating proficiency checks. At our company people get the initial rating on either type and then add the other after app. 400 hours.