Spell Mastery and Path Magic

Should I permit a saher to take the Spell Mastery feat for a mastered path on which he already has the Spell Focus and Improved Spell Focus feats? Could be extremely unbalancing since could have 5 paths under the Spell Mastery feat which could give him the ability to learn over 40 spells without the use of a spellbook.

Probably shouldn't permit this.