West London VW is my Dealership and Twickenham is closely allied to them by coming under the West London VW umbrella. They are both part of the Inchcape Group.
Quite honestly I am rather surprised by the £1k deposit they want. They really should not be requesting this especially for a car that is not in production. Plus, do you really want to be an early adopter? It would be more sensible to wait until the inevitable problems are ironed out and also avoid paying a sky high price as an early adopter.
Finally, to answer your question. They are as good as any VW Dealership, perhaps a bit better which is not saying much as an outright recommendation.
Have you considered RS3? It is beautifully appointed and meticulously made, but overpriced just as the R400 will surely be.