I do use greenstuff for press mould now and then. The trick is using the different puttys characteristics to your advantage. Epoxy puttys though stick to the "cast" really well unless well lubricated. Thats bad for detail but is ok for just pressing blanks of stuff youve done that you touch up after.
Best stuff Ive used so far is the silicone gum type but its pretty soft when cured so detail is usually warped for pressed stuff. It can be quite expensive too unless you have a wife that runs a dental practice and can get decent sized tubs of the stuff
I like milliput for creating little press tools as its rock hard so presses detail perfectly.