Dave

Order still hasn't arrived. No updates from Viking or the courier.

DON NOT USE - SCAM SITE!
Used to change license address, not realising it wasn't actually the DVLA - Thanks GOOGLE!!! Started charging a £39 monthly subscription for a one-off service. Use the DVLA site instead.
Still waiting for them to provide evidence that I agreed to a subscription service.
You can always initiate a chargeback with your credit card company if they don't respond. Then they will have to provide proof of agreement.

***UPDATE***
As of Sept 12th they have changed their website considerably. It now more fairly advises that services may be available directly from the DVLA (with a link) and a banner shows that a subscription fee applies. Of course, they will probably say it ahs always been thus. I have evidence to the contrary however.