"Power is only valuable if it can be harnessed." [Mythos][3.5/PF]

[noob]

Eldritch Wellspring Awakening Shintai
Prerequisite: Character Level 1 only, Con 20

Gain a pool of 100 points of magicka that recovers at a rate of class level + constitution modifier each minute.

The magos converts all essentia into bonus max magicka. They may no longer gain essentia from any source. Whenever they would gain essentia they instead increase their Magicka pool by the same amount.

Expending any magicka prevents magicka recovery that minute. You gain the ability to cast spells. Your spells count as what ever type is most beneficial, arcaned, divine, etc.. Casting cost magicka equal to spell level times the spell's minimum caster level. The spells

As a supernatural ability you may infuse any essentia receptacle with magicka. For every 5 magicka expended the receptacle is treated as if it had 1 essentia invested, up to the normal maximum. This last 1 round per caster level. This increases to 1 minute increments at fantastic, 10 hour increments for legendary, 1 day increments at exalted.

So basically you suddenly have 20 essentia that regenerates but now gains in essentia are divided by 5.
Wait even worse it basically overrides the main class feature of the class or you get two pools and both are in-intuitive.
It is unusual for mythos based classes to make trade offs.