Paintwork Protection - is it worth it?

[Sortie 10]

I am on the point of buying a 2 year old BMW Z4 and have been offered "Silver Seal Total Car Protection" for £249. Seems a lot of cash for what appears to be serious car wash/wax.
Does anyone have any experience of this or any other similar treatment? Is a thorough Autoglym waxing a cheaper equivalent alternative?
Any other recommendations - other firms or diy treatments would be appreciated.