Yes it is very good, nothing complicated about mixing, just get it to a nice thick consistancy and paint it on and rub it in well. Use gloves and mind any gold as it turns a funny colour.
I don't do it as often as I should, really every couple of weeks would be good. Yes they do go yellow, but in the long run keeps them white. If you have scabs it's good to mix some of the sulphur with the like of sudocreme and a few drops of tea tree and apply it, i use the sudocreme lid to mix it. Also don't wash the legs off otherwise you will take away all the good you are doing and the protective barrier. Keep at it and you will see a difference