If you have enough points for Group Demonstration, use it only IF there are more than 10 players over the age of 18 considered grey 2 ball and 1 ball players (which never was any accurate). If there's less than 10, it'd be more economical to scout them once individually.
yes i agree with you, 18 year old player are more valuable then 18 year old player. But i rather take a 19 year old with good skills then an 18 year old with medium skills, because a good 19 old with one season training is stronger then a medium 18 year old with one season training cause the difference in training speed is pretty low.
And even when 19 year old maybe ain#t the option you should go for in the first round of the draft the group demonstration might be a good option basis to get a better second round pick even when he is 19(or an good late first rounder, even when you should go for combine when you draft at this position with active opponents)