Zyneste just about has the right of it. Making a few small assumptions that I won't go into here, we're comparing an base casting PPS of 116.33 to whatever Reprise can put out. Multiply this by the 2.2s recast and you see that Reprise needs to have more than ~256 potency to be worth considering outside of edge cases involving movement. I rounded up to 260. From more math I don't want to burden this post with, we also can evaluate a potency per mana (PPM) based on the melee combo's value, and we can get the same for Reprise. Reprise does not wind up being stronger than the melee combo, in terms of mana value, until you go over about 430 potency. It may look very powerful, but there is a great deal of value in the combo finishers that make the melee combo far stronger than the Enchanted weaponskills alone.

In any cases in that range, using Reprise would still be a loss if you did it without care or thought - but it would also have a lot of value when you do use it carefully, primarily by spending mana you otherwise will waste instead.