The Selden rigid vang we have prevents dropping of the boom onto the coach roof, but will not lift the boom when we need to adjust trim or reef the main. This is where the topping lift has a benefit - but the TL still interferes with the battens when tacking.
I may be wrong, but it's my understanding that a rod kicker, has a pnuematic feature for extending the piston - thereby lifting the boom without the need for a topping lift.
True Blue . . .
sold the Nauticat