Hey, this booster is great, it has being designed and produced by: www.racingtrials.es
The booster has been tested by some riders and they say it is a great booster.
The really good point it has, is that you can set up your hs33 perfectly without the booster, and when you´ve set it up, and it is perfect, then you add the booster.
Also is really light, and the clamps do not need the plastic rings, so it is a REALLY stiff system, and surely it worths it (includes clamps and booster).
You can buy it in the manufacturer´s site, or in trialprod, or in biketrialshop: http://www.biketrialshop.net/index.php?main_page=product_info&cPath=16&products_id=59