I use to do some very custom rides and most of my customers wanted what no one else had. These guys were my spring solution 99% of the time. Send them the stock springs and they will send back the stock springs and another perfectly calibrated set. Sometimes they already have the specs for your truck so they will not need your spring. I always sent the spring to be sure the lowering springs were perfect. Great for any type of spring change you want.
Cost? Well they were usually close to the same cost as a off the shelf set. It all depends on the spring. Great people to work with. Oh yeah, and they are made in the USA by Americans.