[spaghetti]

marwan I've used the Vipers for years and they're really not bad: very accurate for such a lightweight gun. It's designed by the famous Hugues Dessault, same designer of many world's best selling spearfishing gear such as the HD fins, the Samourai mask and many more popular items.
The construction of the Viper is based on the classic french style "arbalete": 28 millimeters alluminium tube, closed muzzle with screw in bands, handle made of a lightweight nylon reinforced with glass fiber, a decent trigger mech with a stainless steel shaft release. The plus of the Viper is a full length sleeve mounted on the barrell, providing a full length rail and some additional mass to reduce the recoil: the total width of the barrell is 30millimeters, instead of the classic 28.
Overall it's a very accurate gun.
The downsides: the trigger is smooth but not particularily strong. You can use it only with a typical european set up: maximum one pair of 19millimeters screw in bands and a 6,5mm shaft. It's not the powerful gun to hunt big Jacks with, but it's accurate and quick for small/medium reef fish (seatrout in Australia?).
Another downside: the barrell tends to leak due to a defective gasket, but you can easily fix it by yourself with a file, a screwdriver and some glue or silicone. I'll tell you how to fix it if you buy it.