I can't compare to any other make, but we use that brand in the salon I work in. It's very good, you can use it "cold" which eliminates some curl/frizz but is not sleek, or "hot", which give the hair the straightened look. Hot is the better option. However, £40 seems waaaaay too cheap. It costs about half that to purchase into a salon and takes around 2-3 hours to carry out the service. In my salon, we charge around £80. It's so lengthy because you have to be so precise. It can often take two people to carry out the service because you can't use clips to hold the hair up to straighten it, (to complete the hot treatment) hence the price. (Time, Manpower, product).
Chemically, the product damages your hair similarly to colour or prelightener. It breaks down the bond in the hair that give our hair it shape, then by straightening the hair it is "set" into place. A neutralizer is applied to seal those bonds back into their new shape. We don't recommend clients colour and chemically relax their hair as it can completely ruin the hair. It's important to use the proper after care too.
Bear in mind the regrowth too, this product grows out, so like a colour, it will need to be reapplied to the roots every few weeks/months, and until you do that, you'll have to straighten that out.
It also takes a week or two for the hair to "settle" after the service - it can be too flat at first, but after a few washes and the smallest (millimetres) or regrowth will help.
Hope I helped!