Tom
I can't say I have ever flown a Magister but I would have said its greatest flaw was not in having ejection seats
.
I think that with its straight wing it would have been a fairly honest aeroplane to pole around. It also had two engines, so it did have a better chance of getting you home than say a single engine Jet Provost, which is what I flew doing my basic training.
I don't know how the performance figures compare in terms of speed, ceiling, range etc. but I guess that the Magister is more comparable with the un-pressurised JP3 and 4 than the pressurised Mk.5.
I think that the Magister might have also suffered from compressabilty issues at say < 0.7M in a descent from high level. The JP5 limiting Mach No was 0.75M.
This may not help you very much but it might help you focus questions to others who have flown both types. I for one was glad to have flown the JP in preference to the Magister though to be fair to the latter it was probably a trainer with a lower operating cost and its lack of sophistication may have been a bonus to many of the customers who bought them.
MB