Some of Brownell's cold blues are pretty good.
I used Oxpho-Blue, 44-40, and Dicrophan T4 at various times.
Oxpho-Blue was probably the best, but I just never found any cold blue to be all that good on larger areas.
Your results will may well vary, but I used cold blues only for touch-up and even then only with reluctance.
One problem most cold blues have is a tendency to leave a blotchy stain in the original bluing around where you applied the cold blue.
These blotches are permanent and can make the gun look even worse on close examination.
However, since unless you have a gun totally re-blued there's nothing that can be used that's better than cold blue, you just buy a good one like Oxpho and hope for the best.