RE windows/doors, I'm sure I didn't do anything like the research being implied above, but having sourced multiple quotes for the same items (one door and one decent size window) in 'crittal-style' aluminium, Colins Sash Windows were significantly cheaper than anyone else who quoted and I'm very happy so far with the products.
it gets pricy if you are after slimline because you either want the look or to try and get them passed for a conservation area, particular building restrictions or a listed building.
Your windows are nice and ‘steel look’ but would not be allowed as a direct replacement for steel in all cases.
RE windows/doors, I'm sure I didn't do anything like the research being implied above, but having sourced multiple quotes for the same items (one door and one decent size window) in 'crittal-style' aluminium, Colins Sash Windows were significantly cheaper than anyone else who quoted and I'm very happy so far with the products.
Pics here: https://www.lfgss.com/comments/16559074/