Well going off the typical magical girl combat time formula
You will have a maybe 2 or 3 battles...with a day or more of downtime before the next volley hits. Until things hit the serious end of the scale when you have to go up against an Army, Midboss, Endboss, and True Endboss all after the other with very little spacing. The meditate time would certainly be something seemingly easy in the beginning, but you're going to be overwhelmed if you focus on it. Unless they get a baddie using their Base school with no forbidden maneuvers, but I think it'd be more likely to find it the other way around.
The forbidden cost is low early on, sure--only one or two per maneuver in the first four levels. So, that's uninterrupted time equal to an entire rest period
after a day of adventuring (which will presumably be needed because of other rules) just to offset using them once or twice a battle. A failed reflex save giving you eight damage at level three wouldn't be something to scoff at, even if you're going the oni route. -5 total HP or so from Immortal Smoke is a bitch, and creates a feedback loop as you rely on it to survive fatal wounds.
Then you hit level five and the costs really start to bite. Use three level three maneuvers, or some combination thereof and a level two or so, between rests and you can't meditate off the whole penalty in an eight hour period of doing nothing else. Higher levels? Only between big adventures is going to make any headway into offsetting regular use.
It gives the GM character hooks and another reason to not allow lots of downtime during adventures, whilst giving characters increasingly big vulnerabilities to target during those adventures. The costs are going to hurt if the GM tries to use them.
