It is what it is. You won't find cheaper than Regatta. It is one of the brands I recommend to the parents of Bronze DoEers as it won't break the bank if the kids discover they hate all this outdoor business. If they like it then they can move up market. Perhaps not for "long term use in extreme conditions" but fine for a stroll in the Cotswolds and an overnighter in a campsite.
Totally agree - its probably better for its price point than stuff from Mountain Warehouse, and no worse than Peter Storm, etc. Its fine for my kids, and I have a pair of their waterproof trousers that I have had for years and its lasted well. In fact one of the best pairs of gloves I've used was a pair of Regatta ones, bought for a fiver from the York outlet.
I suspect the OP has been unlucky in getting a product that isn't quite up to snuff, but I suspect that Regatta wouldn't have a problem if it was a return. However, to be fair, if your paying possibly less than £25 for a 45l rucksack, I wouldn't expect a huge amount from it. Spending double that amount would get a decent solid 45l sack, and at £100, you have some very good choices. You still, to a large extent, get what you pay for.