I mean, everything is subjective isn't it? We can't tell you what is right for you, let alone your nephew.
I definitely type faster on mechs than domes, and I definitely feel less fatigue using the light switches that I love over domes.
And, anecdotally, I gave a Leopold with browns to my little cousins and they both commented pretty quickly that they were finishing papers / reports more quickly and accurately with it. But I also built them a new PC at the same time, so who knows how much the mech had anything to do with it really.
What they really like, though, is that I gave them some KK cats / paws and a colorful keyset to put on it.