The mountaineers route is for those seeking greater adventure, but isn't for everyone. There are climbing sections (like the Ebersbacher Ledges, the section just above Iceberg lake and of course the final chute). If you like the security of a trail it is not for you. I personally love the MR but it is rough coming down on my legs and I feel relieved when I finally get back to the trail
It does have the advantage of being far less crowded. The trail certainly isn't a wilderness experience. Since you approach the mountain straight on you really feel like you went there. The regular trail goes way out of the ways and comes up the back. That is hardly what I see looking at the Mt. Whitney poster hanging on my wall.
I have hiked with Kashcraft. I am sure he was there with his kids step by step, telling them to step here and hold on there. It wouldn't have been easy for them. He has a lot of experience in the area. That is a big help. I wouldn't underestimate the Mountaineers Route just because young people have been there.