I wonder if I am interpreting this feat wrongly or not. Reading the epic feat "Improved Metamagic" it seems to me that, if taken multiple times it considerably outshines the other epic feats that reduce cost of metamagic such as "Automatic Quicken Spell" (191 Complete Arcane) or "Automatic Silent Spell" (191 Complete Arcane) or "Automatic Still Spell" (191 Complete Arcane).
As an example, taking Improved Metamagic three times allows me to cast quickened spells of any level simply increasing the cast level of 1. Whereas, taking "Automatic Quickened Spells" three times would allow me to cast quickened spells without metamagic increase, but only for spells of level 0 to 3.
So I wondered:
What are the limitation of Improved Metamagic (DMG) in comparison to the other 3 feats mentioned above? And, if there are scenarios in which one of the three would be preferred over "Improved Metamagic"?