I don't necessarily see that, at my player's power levels... they'd never be able to place more than one aspect on themselves in a supplemental (-4 to their control would pop them down to +3 or +4 in their best element, barely enough to cover the standard DC)... immediately tapping that for their primary action would grant them +2 shifts to a spell that's already at -1 (from using a supplemental in the same round), for a total +1.
At the cost of not being able to do anything else (like move a zone or juggle), and at the cost of an extra stress (from using 2 spells, so filling 2 boxes).
For an extra stress, they could've gone more direct and gotten a *drumroll* +1 shift by overcharging 1 past their power, and still only be using up a single box instead of 2. Not very profitable when used that way.
Meanwhile, if they used their primary action to set up the maneuvers, they'd be at -1 to do it, and would be able to maneuver themselves 2 single-round aspects. Tagging those on the supplemental would cancel out the -4 penalty... and now they're paying double the stress to break even.
You'd need 10 control and 6 power before you could start to see a gain (cause you can pull 2 aspects at -4 penalty as supplemental), tag both on the main roll to gain +3 (+4 from the tags, -1 from the supplemental). 3 extra shifts is a lot, but you are pinning yourself down by spending your supplemental action, and you are gaining double the stress boxes.
Plus, 10 total control with 6 power already puts you in a solidly strong league. If you're willing to tire yourself out that quickly... I'm not sure I'd stop you... especially considering the same mage, taking advantage of the same rule, could get off a rote attack or defense as supplemental instead, and still probably get better bang for their buck.
It'd really start to get broken with 13 control and 9 power, but at that point... who are we kidding?
As an addendum to my first post- this isn't necessarily something I'd want on the table as a house rule- more likely a 1-refresh ability. I haven't really thought it through much... but it intrigues me, and fills a gap in the books, so I think I'm instinctively like it. I'm happy to be talked out of it with a good example how it can go wrong.
EDIT: Unless, of course, you were referring to the no-stress casting or combo-platter, UmbraLux... in which case, yeah- I see your point, and am taking that off the table. I'm more intrigued by the supplemental casting.