First thing to note is the price! So once you accept that this isn't a £100 electric blanket you should realize that there are some shortfalls. Well the first is that although it's a double size it does not cover a full double bed...not even a 4Ft6", having said that it covers most of the bed just not a foot or so around the outside.
Secondly the material is very thin so you know there isn't going to be the wiring in there to heat it up fast and to a high temp....well having said that it does heat up reasonably quickly but to a more reasonable temperature (which is probably best for most). There is also the added feature that you can use this and sleep at the same time AND it's washable!! On the control pad there is Off/1/2/3/Off.
PROS: does a good job of airing your bed out on a cold night, does heat up to a good level despite what some people say, washable, very thin so easy to put under a fitted sheet, you can sleep and use at the same time, fantastic price for what it is!
CONS: It does not cover the outer part of the bed, slower than others to heat up.
VERDICT: For the price you honestly can't complain, sure it has failings BUT it does the job required in an average time frame, also because it's thinner than most it can be folded down further for storage or transport. For the money i dare anyone to find a better one!