I have used every brand imaginable as an Interior Designer over the last 25 years and here is my findings.
Normal DIY brands including Crown Dulux etc apear 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 infact 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 didnt have any of the old colour left and they still sold that colour. It looks no different where as most barands you would see the difference and end up re painting the whole room again.
THey are also easyier to apply as they are thicker I use a paint pad always it give a flawless finnish then I cut in arround 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.