u can see wat an n1 dual looks like at my cardomain site:
http://www.cardomain.com/id/s14sx2nr
n1 dual is basically 2 N/A version canisters, gets a lot of looks, so none of those exhausts will get less attention than another..hiper and n1 single are pretty much the same thing, and if u dont want attn from the cops, dont get a performance exhaust.....if ure really worried about it.
and as far as i know, theres not a big enough diff in sound to choose one over another...
-Dan