Has anybody used redex fuel injector cleaner? Is it worth using or is there anything else you can recommend ? 

I have on several mechanics authority that they routinely use a service spray at service intervals coz its quick and effective. You can buy such carb/injector cleaners at any auto shop for less than 2 pints of ale. You undo one end of the air feed pipe from the air filter box, and with the engine running, simply spray the fluid down the opening to feed the engine. This will immediately cause it to stall so you have to be ready with a hand on the throttle cable wheel to rev the engine slightly as you spray. 

I'm told this is a better way of maintaining gunk-free injectors than adding Redex or similar.

There is also now slowly being adopted by some workshops, a new expensive toy that completely de-carburises the engine right through to the exhaust end. This can really help with emissions come MOT time. Dunno how much and where though.

HTH