I thought about this for awhile-

As it stands now, the payout for the hashlet prime and zenhash solo are identical.   However, the price between the prime and solo is almost 100%.   The solo won't get the upgrades that gaw is promising down the line, however, its rather hard to put a value on upgrades to happen in the future.    Also considering that all mining does lead to diminishing returns, the time expected to hit the mytical ROI beast we all chase isn't twice as long between the two options, it would likely be 4x's as long (just as a guess, not as a hard figure)   I mean, maybe the upgrades would be amazing and boost profitability, but there is no way to know this.   So given what we know right now-  Zenhash Solo would be a smarter investment then a Prime hashlet.  Right now the only difference between the two is that you can point your prime to a different pool that would pay less then the zensolo.    That's not an added value.   (granted, we don't know the future , so maybe future upgrades would make prime amazing, but only going off what is definately known)