Common chamber is not a big deal, it just means that you can't purge your base fully, but hey, don't burn you seesha and you're ok
But the other thing is, that common chamber hookahs usually come with a really narrow gauaged downstem, so it's hard to inhale with them (harder than with the KM's). If it's a common chamber it's hard to clean inside, and if it's a plated common chamber than it's impossible. On the other hand, quality syrian pipes are made of brass, which is a great thing (the Hafa is made from stainless steel).
(J&R Hookahs have traditional chambers if I'm correct)