Re: Which carb to buy. What is the solution?
r00t, the CNS is a knockoff of a Mikuni carb, specifically the kind that Yamaha used on the PW80 (and probably other stuff, too). The other Mikuni 18mm carbs I'm seeing pictures of (at least the ones that are clamp on and not flange) look very, very similar in design.
Carburetor bowls need venting, that's what those "tubes that go nowhere" are for. The NT carb doesn't have those because it vents through the primer button. The NT carb also doesn't have an overflow; it just leaks out, again, through the primer button.
As for additional fiddling, there are four things to fiddle on with an NT carb - idle, throttle needle, jet, float height. On a more advanced carb, there will be more: add to that the air screw, and a pilot jet (although you probably won't need to fiddle with the pilot jet).
Last big difference between NT and CNS is the choke. NT has a choke cover, which restricts air. This air restriction makes the intake more rich, but reduced airflow over the main jet also reduces fuel, so it's not perfect. CNS has a proper choke circuit which increases fuel only, without restricting airflow, making for an easier start and better lubrication during warmup.