With casters being somewhat rebalanced for the next update, I think the idea behind this feat is worth re-evaluating in terms of balance. There is an issue in that some players can afford to perpetually mana dump, while newbies don't have the resources and can't afford to.
While I like the idea behind "mana dumping", the ability to burn SP at even higher rates than before increases the existing divide between casters with and without resources - based entirely on factors other than skill. A lot of veteran players have a huge reserve of mnemonics due to recent cards or when they were essentially free in the store many ages ago. It also eliminates resource management, which I've always felt was one of the enjoyable aspects of casters.
I think it makes sense to 1) reduce the SP cost of greater ruin and or normal ruin 2) introduce some penalty for excessive mnemonic usage, e.g., "mnemonic sickness - for 30 seconds drinking a mnemonic potions has no effect 3) increase the amount of mana regeneration options available to new players.