The only differences are the number of lasers, power and physical construction. The wrist laser has the strap and body designed for easy treatments in wrist, leg or arm. And it is 5mw. Though the 5mW wrist unit has 5 lasers in total, so overall output power is higher (25mW).The twin has 2 more powerful lasers(7mw*2) that are better for applications in smaller areas such as ear, nose, navel or meridian treatments. Both can treat blood and use the same wavelength of light.