Only Goku and Vegeta aquired this. This form is a state of complete mental and physical perfection of the True Super Saiyan form. In requiring less ki to contribute to maintaining the transformation itself, the maximum amount of ki can thus be focused into the attacks, giving the user access to power greater than that of even an Ascended True Super Saiyan. The key to this state is energy conservation rather than boosted energy output. This results in a saiyan who is able to fight longer and more efficiently than with the Ascended and Ultra stages of True Super Saiyan, and can even remain transformed for days without powering down as long as they don't expend too much energy, essentially making the transformation the saiyan's base form.
A Full-Power True Super Saiyan looks exactly like a True Super Saiyan. The only difference is that the saiyan doesn't always have the aura. Anything the saiyan requires ki to use is colored red.