I still think its difficult to compare like for like. It would depend on the ingredients, its provenance, quality, size etc. Compare sausage rolls for instance you want to read the ingredients and % meat first. Again apples in aldi are horrendous so I have to buy better apples from main supermarkets as everyone complains and they dont get eaten.
I do on the occassion shop at aldi - say olive oil, some veg, squash odd bits but when I shop I go for quality and my bill can be fairly similar to a small shop at Sainsbos.
I agree the cereals are good but the box sizes are tiny and no good for us for the price per 100g is it comparable to a family size of say weetabix which is pretty cheap in Sainbos? Again 1kg own brand sainsbo cornflakes again cheap.
You do spend more at major supermarkets as thats how they work, magazines, endless fruit and veg, homewear, clothing, isles of utter sh"t food etc.
I once bought a frozen pack of salmon portions in Aldi, they were cheap but the portion size was so small and needed the whole packet to feed 3! so not good value. Other disappointing items include bin bags (thin and hopeless), some veg isnt dated so you dont know how long they've been hanging around, baby tomatoes, jam (too thin for us), instant coffee (revolting), chocolate (some good for cooking but far from pleasant).
Good - cereals, oilve oil & quality balsamic, main veg, some salads, cheese, milk, yogurts, tinned fish, washing powder, dishwasher, squash, apple juice, some wines, baking bags of nuts, face creams & hygiene stuff.
You still have to shop at the major supermarkets anyway so you cant really say you will say 20% over the year. The shop is very limited ie you cant get tinned pulses, gravy browning, baking ingredients, wholemeal pasta, brown rice, herbs & spices, decent tea & coffee, certain cereals, quality stock cubes, specialist tinned and deli products.
Got to say I hate Asda, for the experience and quality of some produce.