personally i've used redex a lot on other cars espec. diesels and it does seem to work, it has a delay while its cleaning then it will work after that fuel is gone and the car seems better for ages.
I must admit to not being a fan of car additives, usually if they were that good the manufacturer would use it already, however fuel system and injector cleaners are a bit different because injector spray will deteriorate over time so they can't account for that, but most new fuels have detergents built in so if you use optimax, v-power, city diesel etc then maybe you wont notice any difference?