Our two cents on NTIS: Son went twice. Skipped 1st round the first time and went to regionals, then Cary. Was asked to be on 14u Stars but birthday cutoff changed so played 16u at 14. Made friends, had fun, coach was a nice guy, fair with playing time. Good chance to view NC colleges.
The 2nd time was invited straight to Cary, played well, threw out several. a noted college coach nominated him for the "short list" for the one open catching spot on 40 man roster. The regional rep told son to watch the selection show as it was him vs 3 other catchers, in the end he did not make it.
Was fun to play on USA fields and talk to the college coaches. Nice speeches at the opening ceremony. Son was offered some summer team invites off the weekend. Was invited back a 3rd time but was invited to an MLB team's workout so did not go.
If your son does not have to do all the tryouts (and you do not have to spend the $), it is an experience for your son. Once is probably enough if your budget allows for it. As others said it seems 99% of the team is pre-selected and certain regions are very well represented 
.