I think supplementation with all polyamines is a good one dependent upon the goal and appropriate concentration. Sometimes I do fear that certain proprietary supplements (even those that list doses) are underdosed and people may dismiss a certain compound's usefulness.
In the case of conversion; polyamines all interconvert for the most part...sometimes it is quick, sometimes it is not so quick. Citrulline itself recycles into arginine and offers a more prolonged NO conversion rate. Agmatine's route back to arginine is actually MUCH slower and dependent upon many factors, but the pathway is as follows:
Agmatine --> N-carbamylputrescine --> (putrescine) + citrulline --> arginine
Use of all of these agents modulate different forms of NOS and at different rates (which can more completely be found in the Agmatine thread).
D_