I’m pretty sure the “no clean” just means that no chemicals are left behind that will deteriorate the joint over time. The 951 is the closest I’ve found to a no residue (it still leaves some) which works okay for production stuff because I have control of when and how the joints are made. Wires are soldered on to mcpcbs first and then put on heat sinks VS modding where you may be forced to make joints in a difficult area with parts already on a sink etc.