I think it is too strong against rainbows and too weak against mono. The worst thing about it is that even if your rainbow packs CC, you probably won't have the quanta to cast it.
Then there is the potential for abuse. Certain kinds of quanta, like
, are very easy to get lots of and less easy to spend. With this card, now you can use
for everything including Fractal and Skyblitz
For example: Mark of
, Play templar and leaf dragon, convert enough
into
to cast Fractal, then convert the rest of your
into
so you can play your whole hand of frogs or whatever.