The Dart 18 is a British cat and is raced more in Canada than the US.
If racing is not important, the Dart 18 is as fast, lighter, more forgiving,especially if you normaly have strong winds, less likely to pitchpole. The standard battens can break if you are not careful. Check that the sides of the hulls are firm from the bows back to the mainbeam. There is a foam block in there and the bond to the hull sides must be sound. The rudders have specialised parts which may be hard to come by. You can always buy parts from www.lasersailing.com
Check out www.dart18.com or www.catamaran.ie