Hi!
The Cobra and Highway Hawk kits are almost identical and both are crap. You have to compress and modify the shock itself, which is a bloody hell unless you have the tools. And it is an expensive kit considering what it consists of and the result it gives. The bike will only get 2cm lower, hardly seen at all. The advertisments sometimes says 4 cm but that is bullsh*t.
The Scootworks kit costs more but it is the only kit that actually gives a result as far as I know, haven't tried it myself though. You could get the same result by extending the stock links on your own, which involves cutting and welding (
instructions).
There is another method that I came up with myself while mounting the Highway Hawk kit. The result is exactly the same but you need no new parts, no drilling, cutting or welding. A similar method is described at the bottom of the site I linked to above, but I have attached a sketch showing an even better way of doing it. It's all about letting the locking nut and the U-shaped bracket swith place with eachother, giving a shorter shock. It will also increase the preload on the spring a bit, so you might want to compensate for that with the 7-step preload ring on the shock.