we have HUGE fowler flaps and slats on our BCSC REV2 and it changes the way you fly, I am able to do a full circuit at less than 30kt IAS and at no point does the aircraft feel unsafe.
BUT..... it DOES change the way you fly, you can't just climb into a fowler flapped aircraft and fly the same circuit as you did with a flapless plane, the big flaps affect your elevator effectivity....differently at different CofG and weights, it strongly affects your flare and energy management during your approach and flare, it changes the way you actually touch down and the "feel" when you touch down, it affects the way your aircraft reacts to crosswinds (not necessarily making it less effective it just behaves differently).
so all of these things need to be taken into consideration and the aircraft flown accordingly.
I love having the huge flaps