I wouldn't say you necessarily save money but you do get better quality for your money. Most of the items are slightly cheaper and if you have storage space, worth buying in bulk.
A few things which store well and work out cheaper, based on my most recent price comparison with Tesco:
Toilet roll (48p per roll vs 69p per roll)
Rice (£1.60 per kg vs £1.80 per kg)
Mozzarella cheese (£4.78 per kg vs £9.00 per kg)
Cheddar cheese (£4.22 per kg vs £7.50 per kg)
The maple syrup is also great value although I don't have a price comparison to hand. The famous birthday cakes are super cheap and will feed loads of people.
There are some other branded goods that might not be the cheapest out of all the options but are definitely cheaper for the brand, like Geeta's Mango Chutney, Herbal Essences Shampoo and Conditioner and Prince's Apple Juice Cartons.
I recommend the Krusteaz Pancake mix which is so simple to make up and can also be used for other things, like waffles.
They're also really good for dried fruit and nuts, they sell every dried fruit you could imagine and although they are expensive they work out cheaper per gram.
The cafe is brilliant and I can't think of anywhere where you could get a cheaper meal; it works out about £5 for 2 people to have pizza and unlimited refills. That's if you have room after going around all the free tasting stations.
Make sure you give yourself time for a proper look around; I've got some great deals on toys, spirits and household bits. Don't take your children, they will want everything, and you'll end up spending loads of money on terrible UPF filled biscuits and cakes that they begged for, and then claim not to like when you get home.