I always look for the old St Michael labels on clothes in charity shops - they're generally much better than modern M&S clothes. The sizing was consistent: I can buy my usual size without trying it on and be confident it will fit. Nowadays their sizes are unreliable like other shops and the "short" length in women's trousers is still too long for me (sometimes just a little, sometimes a lot) whereas the St Michael short length fits me every time. They also had sensible washing instructions, e.g. almost everything was machine washable and colourfast, but nowadays if machine washing is even recommended at all it's all "wash with like colours" and they often do run in the wash, and are more likely to need ironed. The overall quality and durability was usually superior in the St Michael days too, and I tend to prefer the styles.

Their food is usually nice: it can be a bit pricey but if you compare like with like (e.g. the posher own brand equivalent in other supermarkets which do cheapo, regular and luxury versions of various foods) they're not really much more expensive, if at all, for a treat - they just don't do the cheapskate option for most stuff. That said, some staples like milk, bananas and baked beans are typically about the same price as the big supermarkets.

I remember when some other shops introduced special shopping times for sensorily sensitive customers, with softer lighting, no music blaring, no staff filling shelves blocking half the aisle, etc, and I thought it was a good idea but also a description of a normal shopping experience at M&S. Supermarkets usually have harsh, excessive lighting with at least one (often several) malfucntioning fluorescent strip light flickering visibly, and as a chronic migraine sufferer I do appreciate M&S' more user-friendly lighting, though I still do most of my shopping elsewhere since I'm usually looking for a wider range of cheap food (it's sometimes worth going near closing time for the yellow-stickered stuff though).