I'm tempted to buy a used car warranty like the one advertised on here but are they any good?

Got a mondeo with a shade over 50k on the clock and a bit worried about the dmf, nothing wrong at the mo but who knows. Would this be covered by a warranty?

Any advice appreciated.

Yes they are good, however sometimes they are not. Most warranties wont surpass 75,000 miles or 100,000 miles, so you could pay for a full warranty term, and get only a fraction of the coverage. Warranty Direct I have used in the past on a MK6 Fiesta and it was worth it, I got various pumps and pipes replaced for a £50 diagnostic fee, saved myself a good £600, and I only paid in a small amount. HOWEVER!!! you must bare in mind that SOME providers out there will treat this as a "pay as you go" system... If you havent paid them the amount in your monthly premium / overall premium - to cover the cost of the warranty job including labour - then there is every chance you will be charged on top...