One other difference that would be a major factor to me is that the Smart Tec has to be sent back to the factory for battery replacement. I consider that unacceptable in any case, but on top of that I have heard stories (and have no personal knowledge if it is true) that Scubapro has previously stopped supporting some older computers leaving users with useless computers that would work okay i they could get batteries.
So, just how huge is the Sol/Luna? Is it really too big to wear on the wrist? Nothing wrong with wearing it on the forearm I guess, so long as it stays there and doesn't slide down.