More generally, these techniques are called instrument assisted soft tissue mobilization techniques (IASTM). There are many adaptions of IASTM, e.g. Graston Technique, ASTYM, ASTM, STM, ISTM, FAKTR, FAKTR PM, SASTM, FAT etc
They all have their own little variations, however, differences are very small, because they are overlapping each other. E.g. they use movements while stroking, they vary tissue tension during stroking etc. However, all these techniques use many different protocols which can be defined as different subtechniques, e.g. peripheral nerve releaseing, breaking up adhesions, muscle spindle resetting etc. Bottom line is, that look for IASTM, you'll get more results while looking literature.
Copied text from mikept's post's in physiobob forum:
Studies mostly so beneficial effects. One showed no effect. Methodology between studies differs, different instrument assisted techniques were used, results aren't 100% comparable.
• 2 minute treatment and significantly improved ROM, even better than foam rolling (FAT technique):Acute effects of instrument assisted soft tissue mobilization vs. foam rolling on knee and hip range of motion in soccer players. - PubMed - NCBI
• significantly increased ROM (IASTM): Acute effects of instrument assisted soft tissue mobilization for improving posterior shoulder range of motion in collegiate baseball players. - PubMed - NCBI
• increases temperature (graston technique): Comparison of blood flow changes with soft tissue mobilization and massage therapy. - PubMed - NCBI
• decreases pain (gua sha): Randomized controlled pilot study: pain intensity and pressure pain thresholds in patients with neck and low back pain before and after traditional... - PubMed - NCBI
• fourfold increase of microcirculation (gua sha): The effect of Gua Sha treatment on the microcirculation of surface tissue: a pilot study in healthy subjects. - PubMed - NCBI
• some found no effect (graston technique on calf muscles):http://www.ncbi.nlm.nih.gov/pubmed/25347141
• increases tissue perfusion and alters microvascular morphology in the vicinity of healing knee ligaments: http://www.ncbi.nlm.nih.gov/pubmed/24073942
• accelerated ligament healing: http://www.ncbi.nlm.nih.gov/pubmed/19574659
Nowadays, this field includes even more techniques like fascial manipulation, Gua Sha, Cross Friction etc. New IASTM tools are adapted for using many techniques, it's not only one technique.
How to compare these techniques with massage, gua sha?
They are very different, IASTM has very concentrated mechanical pressure and works differently than massage. Gua sha's goal is also different, however, some if it may be similar. It's really hard to compare these techniques, because IASTM-like techniques include so many sub-techniques.
I use many different manual techniques in my practice, also many IASTM techniques. I would say that IASTM has it's unrerplaceable place in therapy, for example thight plantar fascia, releasing peripheral nerves, mobilizing immobile tissue. It's like with every technique, no technique is universal and you always need many techniques to treat patients. IASTM can't be the only technique in your arsenal, still I would say, it is very useful if it is in your arsenal.
Sorry, my answer isn't the best. IASTM is a practical technique, you'll get better picture if you try these techniques, specially if you try these techniques with different conditions. Few IASTM tool manufacturers have manuals, which include many of these techniques, buy their tool and you'll get more clear picture of IASTM.