Graston is significantly different than guasha, though the appearance of the skin after treatment is similar.
Graston focuses on scar tissue, and sinks into the adhesions quite deeply, often near a bony prominence to get additional leverage and "break" the adhesion. It's nearly always focused on a particular area (or 2) of injury. It is very intense and often painful.
Guasha opens up the superficial fascia, whether there is scar tissue or not, is gentle (though it looks scary) and is not looking to "break" anything.
Mick, the red marks are pettichae, not just vasodilation. The TCM view is that it is "sha" or very simplisticly: blood/qi imbalance. The color and depth of the sha tells the practitioner what imbalance is presenting, ie: blood stasis, blood deficiency, qi seforum.xxxnation, wind invasion, dry blood, excessive heat... (all TCM concepts of course, and not at all like our western medicine.)
On a purely biomechanical level, the technique it most resembles is intense myofascial release.