For a start, that one is not for a Golf 2l 8v.
Secondly, as Ess_three found out after lots of dyno testing, they don't add any horsepower, the standard manifold flows well enough up to 200hp.
Thirdly, a lot are made for LHD cars, because in Europe, the LHD market is larger than the RHD market

Fourthly, they don't have a flexi joint, so you'll have to fit one unless you want to break the exhaust system in no time.
And last but not least, getting them to fit on the head is sometimes difficult as they can be made of the wrong measure but a few mm.
Conclusion: Stay away from them, if you are adamant of buying one, get one from a well known reputable brand.