I've been known to buy it on occasion and take forever to use it because I keep forgetting it's there. I'm no expert but would hope that any well known additive manufacturer ought to have the resource to be sure the product does what it says and stays beneficial to today's vehicles. (And others warn against because they want to sell you something instead. ) So I would doubt it does much harm. Unsure how much good it does though. If you've already bought it I'd suggest using it.
Having thought about this a bit more.....Redex dates back to before we had top quality petrol (and all those marvellous additives) and before we had catalytic converters. I'm wondering if adding Redex is going to be that beneficial to the catalyst?
I used to use it (got my first car in late 1968), but I never really knew if it was doing any good. I kept that car for 10 years, so was it due to Redex or just careful driving and regular servicing?