Comparing the stats of all the weapons and the trends they have between levels, I'd say their stats are great and they are worth the time. (also, noone can say what else they will boost. will Spirits Within damage be doubled? Will Flare's DOT be trippled? etc)
The Relic weapons are equivalent to melded Lvl 60 weapons (by comparison to the highest lvl 50 crafted weapons), yet you can use them @ lvl 50.
The Primal weapons would fall into the range of lvl 55-56
With the idea that a IV materia in essense increases a piece of gear's level by 4 (and III by 3)
a weapon with IV, III, III materia's would give you a Relic Weapon.
I'd choose the Relic over a Tripple melded weapon, cause they look sweet and cause I hope they add a 6 piece AF bonus