After doing the TWM shifter on my car, I can say I'd do it again. I really never like the 2nd to 3rd shift in this car in particular, and after the TWM shifter, I can say that is greatly improved. I couldn't bring myself to spend the money for the TWM shift knobs. I bought a Voodoo shift knob to start to see how I liked it at first. I think it's fine and $100 cheaper.
It's a quick easy install really. I think the people that say it's not worth doing because the Z's shift throw is already pretty short, haven't driven a car with one. As far as Z modifications go, it's not horribly expensive, and it really does make the shifter feel more precise.