So shortly after I got my 0.5 Tect 2 way I ordered the 0.7 and 0.3 versions, then the Light 0.3 and 0.5.
After a month or so of using them my preferences have changed. I find it extremely difficult to use a 0.5 for doing calculations, and 0.3 is ok for writing. I prefer 0.5 for writing / taking notes and o.3 for calculations. However, the 0.3 sees plenty of writing action, since the small size makes it ideal for exponents and subscript letters.
The Light version is cool, but in black looks somewhat cheap, the white one looks better, and it's easier to use for long periods of time due to the weight, but for general use I like the regular / heavy one.
Also, Zebra has recently released two more colors for the regular version, black and red.