I have used every brand imaginable as an Interior Designer over the last 25 years and here are my findings.
Normal DIY brands including Crown, Dulux etc appear to much thinner, ie the coverage is poor so you have to use more coats, If you work out the time extra and that extra pot at say only another £19.99, you will in fact by using the likes of F&B and a few choice others be actually saving money by using a more expensive paint.
Also, a more expensive paint can be rematched easier. I had some french grey in my lounge for 4 years and I did some plastering on one wall after creating a doorway, I didn't have any of the old colour left and they still sold that colour. I repainted up to another wall adjacent and It looks no different whereas most brands you would see the difference and end up repainting the whole room again.
They are also easier to apply as they are thicker, I use a paint pad always! it gives a flawless finish, then I cut in around the edges.
I used F&B French Grey in this room in the beautiful 500-Year-old Farmhouse.
We won BEST COUNTRY HOUSE with this in 2016 with Period Living.