Don't know what's in the first two. However, Rally contains acriflavine, and I've had pretty good success using that (in a bath treatment) to treat both brook & velvet before placing the fish in a QT with CP. Acriflavine is not as harsh or toxic (non-carcinogen) as formalin, but in experiments I've done comparing the two side-by-side results were the same.
Yes, I've read this too, but I've never tried it.