The genuine interface can be bought brand new for just £250, not sure where you have seen the £400 quoted?
For your money you get free lifetime support (via email) and free updates every few months, it costs a fraction what the dealers VAS / ODIS costs and yet it will do equally as much if not more. (
VCDS can do certain things the dealer stuff cannot and vice versa)
However anyone can download the software without owning any cable at all, the software is free, you just can’t connect it to a car successfully without a suitable cable.
Not to mention the R&D that is constantly being put in.