Allianz is a well-respected 'major player' in the UK insurance market (with an annual turnover in excess of 1½ billion pounds). It was voted General Insurer of the Year in the 2010 British Insurance Awards. So there's no reason not to trust the company.
However I'm amazed that you seem not to have encountered the advice which is consistently being given out by the Consumers' Association, BBC Radio 4 ("You & Yours", "The Money Programme", etc) and BBC TV ("Watchdog), as well as in the consumer sections of all of the 'serious' press. Such advice repeatedly states that insuring electrical products against breakdown is both largely unnecessary and ridiculously expensive. (Sales staff usually earn much more commission from selling the insurance than they do from selling the actual product). The advice which is constantly, and consistently, given is that customers should NOT take such insurance cover. Instead they should buy from a reputable retailer and rely upon their statutory rights (which last for a minimum of 6 years from the date of purchase).
Chris