The aftermarket ones are not as stiff as the original. The type 2 Wolff is just a bent type 1. The bending gives it less preload with the same strain screw setting, therefore a lighter trigger pull. Also, the "Power Rib" goes down to where the strain screw fits into it, effectively giving you a shorter strain screw.
The Wilson spring is a bit shorter than the Wolff or S&W. This pulls the stirrup more parallel to the rebound slide, giving a lighter trigger pull with an equivalent hammer pull. The others pull the stirrup up at about a 45 degree angle, and it takes more force to bend the spring downward as it goes forward. The Wilson spring only has to go forward without bending down.
I use a #8-32 socket setscrew for the strain screw. A 3/8" long for round butt or a 1/2" long for square butt. The setscrew must be retained with either #222 purple Loctite or #242 blue Loctite. Doing this holds the screw in place, but allows easy adjustment or removal at any time in the future.
For those who want a regular strain screw with a head, you can use the setscrew to adjust to the spring tension you want, measure the hammer pull weight with a trigger pull gage, and shorten one strain screw to get the same hammer pull weight. Then you don't need a big pile of strain screws, just one.