I have a Geissel Super Dynamic - Enhanced on one of mine now. Very similar to the SSA - Es but with a flat trigger and 2.3 first/1.2 second stage pull weights.
I've tried singles and doubles and, given the choice, would not use a single again. The first stage pull offers a short smooth take up to a definite stop at the second stage. At that point a very gentle pull thru a glass rod break drops the hammer.
I find it makes the shot MUCH more predictable. It does add to safety, particularly at sub 1 lb. trigger pulls, but I'm in it for the feel.
I have a Remmy 700 with a massaged factory single stage. I'm looking for a way to convert it to a 2.