I had a couple of pairs of HFX-Mag and HFX-9 brakes “back in the day”. They were very reliable and dependable with good stopping power in all weathers. I rode these brakes all over Canada and Europe with no issues, including much longer descents than you’d ever enjoy in the UK.
The brakes were fitted with Dangerboy CNC brake levers which much improved the lever ergonomics. The MC piston rod benefited from being loctited to the lever barrel to stop it migrating under vibration.
As with any DOT brake, after a season or two of hard use, the pistons would start sticking and the calipers would require a rebuild with fresh pistons, seals and high-temp silicon grease. Once done, brakes were good as new.
I was then unfortunate to have a set of Hayes El Camino which literally never worked properly. Neither myself or the UK distributor could get them to work, they were replaced with an early set of Avid Juicy brakes which were excellent.
I don’t understand how Hayes (even as part of the wider group) is still going as you never see their brakes, unless their automotive division floats the brake business and the MTB side is a small diversion?