Is £300 for paint and upholstery protection on my new Mazda 3 a good deal?

I've just ordered a new Mazda 3 2.0 in silver. The dealer offered me Safegard paint and upholstery (cloth seats) protection for £300. I've never had this done before since I look after my cars. I have some Autoglym Super Resin Polish and a tin of Meguiars Mirror Glaze Professional wax. Does the Safegard treatment offer any useful advantage over what I can do myself with the products mentioned above? If the Safegard treatment is worthwhile, what's the maximum I should pay?
The dealer is trying to make some of his profit back by selling paint protection on which he probably makes £200 commission. It's probably worth £200, leaving him with £100 on which to feed his family. I personally favour Autoglym High Definition Wax (not 'polish'), a good coating of which lasts 6 months to a year.
Answered by Honest John

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