My experience of the headgasket kits is as follows:
The headgaskets are genuinely good (often Elring or Payen)
The cam seals are awful (re-use the originals)
The exhaust manifold gaskets are the wrong type (often composite)
The cam cover gaskets are not upto scratch (so I use genuine, have tried LOADS of different types and there the only ones that last reliably every time!)
The dowty seals are often not great
The inlet seals dont fit (but thankfuly the originals will be fine).
You need the O ring for the water transfer pipe (rear of block)
The manifold to front pipe gaskets are usualy ok.
I got to the point where I bought the headgakets and bolts online, the dowty seals and cam cover gaskets from a genuine source, I usualy replace the stat whilst in there which I get online. I also re-seal the oil cooler so used the loctite sealent (which is not pricey from Vx) plus the Vx aluminium O rings (again, not pricey).
As for the comments re 'genuine', the above is based on experience, learning the hard way.....so come back and re-educate me when you have done 10+ and seen them with 50-100K miles on them.