I and my colleagues teach IASTM techniques to my students concurrently with manual therapy techniques. First of all, instrument assisted soft tissue mobilization (IASTM) is one general term for many different techniques. It's not only one specific technique.
Effectiveness
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
Instruments can assist variety of soft tissue mobilization techniques, cyriax cross friction, gua sha, peripheral nerve and tendon release, muscle spasm treatment, functional techniques, scar mobilization etc. Few of these techniques are registered with different names like Graston Technique, ASTYM, SASTM etc, however, all of them are basically IASTM.
What do I think about these techniques?
First of all, they save my hands and time, because protocols for these techniques are very short. Techniques are very easy to learn. They give you additional option to assess soft tissue (through instrument's resonating). Allow to implement more concentrated treatment and mechanical pressure, incomparable with hands. Finally, starting with these techniques wouldn’t cost more than few bucks, however, those cheap plastic tools have their limits.
Conclusion
Instrument assisted techniques have lot to offer to musculoskeletal manual therapy, more studies are needed with more similar methodology to find more focus for clinical effectiveness (which exact conditions are good to treat with these techniques).
To ethanl: find a all-in-one stainless steel you’ll like, prefer tools that are designed for multiple techniques, many tools come with a guide or a manual. There are hundreds of tools available, few examples:
from simple http://www.starrtool.com/
to more advanced http://www.physioneers.com/ and http://www.tecnicagavilan.us/purchase/
to instrument sets https://www.grastontechnique.com/CartUSA2.html