Tyrone,
Graston and ASTYM are essentially the same form of treatment with slightly different tools that fall under the category of "Instrument Assisted Soft Tissue Mobilization." It's a helpful style of treatment, but is only as good as the practitioner. The tendency as I've seen with IASTM is that many practitioners are attacted to the bravado of the pettechiae (breaking of capillaries, bruising, etc) and do not necessarily appreciate the physiology of the tissue and that of the stress response. It tends to be more "gross" in nature.
Physiologically, IASTM can mobilize fibroblasts (lay down new connective tissue), reinstate inflammatory processes (this is good in the short run), and, with appropriate other treatment, help the healing process. There are a handful of case studies where multiple interventions including IASTM have resulted in good outcomes for tendinopathies. From studying with some of the "major" IASTM schools of thought, they seem to be quite "mechanical" in nature and fail to appreciate pain science of the 21st century. It doesn't mean it doesn't work, it just means that it may not work entirely as its explained.
ART--a more complicated, and somewhat different version of pin and stretch, is, too, yet another tool that depends heavily on the practitioner's grasp of palpation and their understanding of the physiology of manual therapy. Physiologically it offers important benefits that overlap those of IASTM to a degree. It is more specific. Where I dislike their approach is in their recognition (or lackthereof) of pain science and pain generating sites. It's a great tool.
All listed are just commercial tools to get a job done. What I'd suggest is to "shop around" for good therapists. Ask them how long they've been working with particular techniques, have they treated athletes, have they treated your injury before, were they successful, yada yada. Be on the lookout for somebody who doesn't tell you they are ART/Graston/ASTYM, but instead practice multiple techniques--soft tissue, joint mobilization, exercise, etc. See that they have a passion for learning more within their trade.
Regards,
Carson Boddicker