I feel that the Vong bowl is scorch-prone but the M bowl makes a fine replacement: better flavor, big hits great for water. The M+ is more aggressive than the 21 M, so again, good for water. I like the '21's airflow a lot better, though. I usually use it mostly but not entirely closed thru water (still need a little airflow), and yes, it's because of the 14mm joint that I've put them together: the voluminous vapor production is ideal for water or whichever extra cooling you prefer.
I go medium grind, straw pack, light tamp. I'm not sure about your second question, I use the full bowl mostly but I have a couple dedicated half-bowl tips. Packing it looser seems to work fine, as well.
The M+ bowl is pretty flexible and I think it produces very well. I haven't tried the 9-fin yet but I hear great things. It is twice the price, fwiw.
Great solution. The standard joint opens it up to a world of possibilities.
I think it's the increase in density that people are after, but pulling air through the tip alone cools the herbs, the tip, and the cap faster, leading to less actual production, but less dilution too.
Your observation is well supported. I mostly hit it hard, airport open and get huge hits but slower can be cooler. I don't use the airport much at all, except for that last whispy hit I'm trying to squeeze out. George explains: