Very hard at this time of year. The headers probably have one of the hardest lives on the bike, going through extremes of heat cycles and getting the road grime blasted straight at them.
If you ride only in the dry you're doing ok, but if you use the bike in all weathers it's hard to keep them nice. Most people simply give them a spruce up now and again with some caustic cleaner such as Harpic, but these can be quite aggressive and nasty to metals like aluminium if you happen to splash it around.
A scotchpad with detergent can work well IMO and then a polish with something like Autosol, but either way, expect a bit of elbow grease to keep them looking top notch.
Just sponge on hot soapy water after every ride, regardless of weather.
Never put bike away wet, dry off headers and spray on something like wd40.
I personally would not use anything abrasive or caustic on chrome if you want to keep it.
I can't imagine ACF50 working well on headers. It's basically a sticky oil based coating and the temperatures the headers get to would most likely cook it and leave a black mess on them rather than leave them nice.
Elsewhere ACF50 is fantastic stuff however. I've used it on previous bikes and ran them through winter. A clean up in spring and they came up really nice.