Here's my take
Retayne sets the colors. You would use this to set the die in your fabric, before you cut the fabric. This should stop further bleeding and keep the strong fabric color.
Synthrapol keeps excess die shed in the water, in the water, not deposited back on the fabric. This again stops further bleeding, but in a different way. The fabric color may be slightly lighter when you're done because you are basically washing out excess die. Usually before you cut the fabric, but you can use it on completed tops too.
Color Catchers are similar to Synthrapol, draws die bled in the water into the color catcher so it won't get deposited on another part of the quilt. Usually used with completed tops.