I used Warranty Direct for the first 3 or 4 years of owning my GTV (which was 2.5yrs old and 20k miles when I bought it). It cost between £600-£700 per year but paid for itself because of the wear and tear cover so all the things that normally wear out on Alfas in that time were generally covered, plus a few one offs like window regulators, ECU. It was also my daily transport then doing about £12k miles a year. Had a few arguments with them over claims, eg, they wouldn't cover worn out shocks (how is that not wear and tear?) & they were quite tight at times (well, they aren't in business to give out money after all ...). Stopped renewing when mileage got to 60k so I had to pay a %age and also my annual mileage dropped to 4-5K. Having replaced all the major items & doing less miles things aren't wearing out so much and I no longer need it.
£425 is much more affordable but if you are doing low miles and major items are reasonably recently replaced then might not be justifiable. They certainly don't cover everything (eg, clutch). Check the list in the policy documents.