Shot One,I fly A320 family & A330,mostly v.similar apart from obvious differences ,size,+ ground handling characteristics &landing flare the Airbus philosophy is workable.However some systems ;notably hydraulics & electrics do differ substantially so good training & awareness are vital.I believe most competent pilots can operate different types under normal conditions & in a familiar environment,but if it all goes pear shaped...? that to me is the acid test: as you know the A320 is a short range ac ,the A330 isnīt sh vs. lh can be very challenging.I have no experience on mixed Boeing flying ,but I do believe any mixed fleet flying increases risk,Iīm not saying itīs unsafe at all ,but we must be aware & manage the risk.Thatīs all ,hope this wasnīt too boring.Yours Cisco