Those "warranties" are not worth the paper they are written on. Lots of exclusions, attempts to wiggle out of each claim etc etc. Better just to put some money away, or have an overdraft/credit card for in case something happens than to rely on those crooks.
AA & RAC warranties are actually very good, my RAC one paid out almost £1k just a month or so after I bought the car 2nd hand. Only thing I had to pay was diagnosis costs which was fair enough and labour fees if over £55 an hour, the garage I chose billed at £55 an hour
Back to the Zed, if the OP has driver a few hundred miles with low oil level, why all the doom mongering? The car could have been driven for months with no oil and then filled up and he would be none the wiser
I think the best advice is to get it serviced properly and get a decent 6 month warranty for a few hundred quid and enjoy it. If all is good them great, if it goes bang then you get it sorted