Rarity. No really, that's it... Okay, so technically the baseplate is slightly different being in the style of the older RFB but they shave exactly the same so its nothing to lose sleep over, I just think they look nicer
The slight difference in the weight of the head is made up for by the very small differences in the handle (which is very slightly longer than a normal Fat Handled Tech, hence the balance is not noticeable.
They're great razors and the shaves between the two are identical.