Just like Engagement, Enchanted Reprise's only use is to fit into a specific niche scenario to let you keep consistent uptime.

Example: Targeted by Innocence Tether, Swiftcast on CD, using Enchanted Reprise is better than just running to where you need to be without casting anything.

It's not meant to be a tool to spend excess mana, or to be a DPS gain on its own. It's basically Scathe, and you want to avoid using if possible, but to use it if necessary.
The only real issue is that it does delay your next melee combo, which is pretty punishing.