The ones I got of ebay, are perfectly alright. The lock works well, the mount is metal and good tight fit with no free play, the internal finish is matt black and completely non-refelective. Seems to me that a lot of reviewers slate products without actually trying them first or they look for something with a much tighter spec. Okay the likes of Kenko is well known and established but that doesn't mean the cheaper alternatives are any less well built or inferior in quality and performance. There probably are some real cheapos that are poorly built and don't have refinements to make them good quality. The problem with most online sales is not being able to handle the goods or try them before purchase so we only have comments and reviews of online posters to rely on which in itself can be some what tricky as we all have different ideas and objectives to what makes good quality and value for money.
I still say that Branded makes probably cost a lot more than they really need to and in lots of cases one is paying for a name rather than a functional product. I think the main advantage of chosing well known brands is consistancy in quality and established support networks and after sales service, although there are many instances where well know manaufacturers have had problems. If you can justify spending upto 3x the cost then chosing the well known established manufacturer is probably right for you but should always remember that its worth checking out cheaper alternatives.