Smack: some people use the topping lift as a sort of anti-vang, to induce draft on very light days by counteracting the weight of the boom & downward pull of the mainsheet. Lift the end of the boom, sail gets fatter. Emphasis here on "very light days." A rigid vang on a C22 is a bit odd: it would cost half the market value of the boat.
It's like a hydraulic backstay adjuster -- cool, but overkill where a 3:1 tackle works as well. There's a neat alternative to a full-on rigid vang, tho -- the Boomkicker
. It's basically a sprung batten that behaves as a topping lift & works in conjunction with your existing vang.