But as i understand it players with 5 balls have a slight higher probability to be higher on the list then those with one ball.
Of course, otherwise the lists would be totally random. :)
Just to give an idea, in my experience, you can expect about 50% of your 5-ball prospect to actually have a 5-star rating, while the odds decrease to 25% for 1,2-ball prospects. Not a huge difference if you're looking for a great player, and considering the cheapness of Group Demonstration.
The real difference is in the average rating, as you can expect a lot of awful players to pop up after group demonstration. I'd say that 5-ball prospects actually hide an average rating of about 4 balls, while 1,2-ball prospect have an average of 2.5 balls.
Additionally, I'm still convinced that, assuming their rating is equal, prospects from the top of the list tend to be better overall than the ones from the bottom (i.e., they tend to have a higher potential when you scout them twice). I do not have a clear evidence for that, however.