I have no idea what are they. Are they some kind of custom objects like bones, or they give some special effects on bones, like custom moving/scaling/rotating and such. Please give me excample for what are you using them. Oris ik solver useful at all.
In my studio, the most common uses for IK's are for legs and arms. We do a lot of animals. If we are doing a creature that uses multiple joints when it walks, like a horse, we typically use a spring solver. But for things like a tail or elephant trunk, we just use driven keys to control the bend and swing of it.