By "authentic" I'm assuming you're referring to licensing. I am pretty confident in saying that I don't believe either Knoll or Herman Miller sells any of their goods through Bauhaus 2 Your House.

I'm not saying that B2YH is no good - in fact, I have the Robby coffee table which B2YH sells, which I purchased years ago from DWR at clearance and like it. But those egg chairs at B2YH look terrible - really cheap looking.

Just by looking at the pricing and their "About Us" page, I'm betting that they're sourcing from a quality manufacturer with a factory in Italy - perhaps Gordon International:

http://www.gordoninternational.com/directory.htm

..but definitely not Knoll, Herman Miller, Cassina - or China.

that's a knock off saarinen- 3 ways you can tell:
1- Knoll does not make a black laminate.
2-Knoll coats there marble in a microfilm of polyester sealent (totally worth it for the added price, marble is a very soft stone)
3-it says "made in italy"-- if they put that on there and it was Knoll they would have said so.

I'd love the Robin Chair, by Allison Smithson.

But buy the Knoll if it's domestic, buying 'local' would reduce your carbon footprint and help keep our economy going. Or just get a knock off from a used office furniture place if you get really lucky.

so is Gordon International good quality?

I think it's interesting to see that the italian-made "knock-offs" are not that much cheaper than the Knoll, Vitra, Herman Miller "orginals". I don't think one can judge their quality from pictures, so hoping for a few more first-hand accounts here is probably the right strategy. But even if their quality matched e.g. that of Herman Miller, one probably would still want a more significant discount than they provide.

On the other hand it's nice to see that they have a few designs that one doesn't get everywhere else.

I work in a store that sells Matrix (matrixinternational.it) that looks to me a quit good example to don´t buy just a label. Their products speak for itself and they were suppliers for an important brand till they started producing under their own name.

The "originals" are only a question of commercial and marketing interests...it's true that there are some editions who are not worthly and who do not respect the original design, but if you look and research carefully you'll find some very good quality suppliers.