I already have one of these that I bought from Costco for £63 (in store), it's £73 online delivered - http://www.costco.co.uk/view/p/energizer-lithium-polymer-7500mah-car-jump-starter-199996
Note the Costco one comes with a bag to keep it all in, the one from Aldi doesn't but if you're not bothered about that I think this is a good deal. The next cheapest place for this ignoring Costco is Argos for £90.
I have used mine a couple of times and it is brilliant for the size. Be aware it's no miracle worker, it will jump start a battery that is a little flat which won't turn the engine over but not one that has drained alot, it's no substitute for a good charge.
Also good for charging mobiles and tablets etc.