The neafl rules allow the four afl clubs to add up to 9 non drafted 19 year olds to their list. They then provide the main top ups. The club can also use cat b and academy rights to draft them if they wish. I think sam wicks was the first to be drafted from the nds, although jake brown might have as well.
I think the rules for kids prior to their draft year training with the club are quite strict, whereas post draft year they can. As a consequence the nds will do a pre season with the seniors.
Is it good to do the nds? There are pros and cons. It can be pretty crap being a top up depending on the nature of the listed players. I think this year there are quite a few first year swans players and so the nds guys have been well included. Of course what happens on tour stays on tour but I think they all had a great time in darwin!
In past years the neafl has had a lot of older players who were fighting for senior spots and their careers and so being an nds wasn't much fun. About 2 years ago some of the listed players were horrible to the top ups. Fortunately they got delisted.
Now the squad is a combo of young guys, and some awesome people like kieran jack. Being able to play with someone like kieran jack is something some of the nds guys will treasure.
The downside of the nds like anything is where a player starts to realise they probably will not get drafted by the swans. That tends to happen about now where some nds don't get picked for neafl and under 17s and 18s start to get a run. This happened last weekend and I saw kinnear beatson at the neafl to check the younger ones out.
I always feel very sad for the young men who have devoted so much time to their passion only to see it not reaching fruition. However if they are really dedicated don't give up. Go to the sanfl like lower, go to the vfl. Fortunately there are multiple pathways.