Yes, they would resist, but with the mouth-suction option it is over MUCH quicker, because you get the mucus out VERY quickly. With ours, no more than 2 quick sucks.
My friend's daughter (at 3yo -when she still couldn't blow her own nose) would actually bring the nasal aspirator (mouth-suction one) to her mom and ask her to do it. I don't know what my friend did that her daughter not only not resist, but actually initiates it.