There have been some posts about this and you will always get different answers from ams and pro alike.

There are sooooooooooooooooooooo many clubs out there that it is impossible to try them all, demo them all, read about them all, search for the best deals for them all to try to pick only one.

What I can tell you about knock-offs is this:
They hit the ball.

What I can tell you about proper manufactured clubs is this:
They hit the ball better and more consistantly. You will find that the manufacturer has better materials and fault tollerences. This translates to a 7i being a 7i and not a 8.5i. That is about 5 yards. If your 6i was a true 6, then you will have a gap of 15 yards from your 7i and your 6i. You will notice that and wonder why you can "never hit your 7i".

I hear it all the time. So, be careful of that.

The knock-off market is good at copying the look of a popular club. This is perfectly legal. What is illegal is the manufacturing of the shape using the same materials to within a degree of closeness. You will see that the club will resemble the real one, but if you place them side-by-side, you will notice major differences. This are the ones worth patenting that make that club better and unique.

I have allways said that it is better to find a late model used set for the same price as a new current model knock-off. You will get later technology, but it will be good technology.