MT was a barely useful prestige in D&D 3.5 where classes didn't have class features. In Pathfinder you lose a lot of class features in addition to caster levels when going MT. It is not a good choice for any build. Most pure casters will be better than a MT. And something like a Scroll Savant is better than any MT you can come up with.
There are several classes without much in the way of class features to lose an
d through much of the game there are more rounds between rests than there are spells in a single spellbook.
There is also the matter of getting more useful touch spells into the Magus spell book* and spontaneously casting whole spellbooks.
* - you can Spellstrike Slay Living with Tristian, for example
Ho hum, another day of negative theorycrafting with the old farts at RPG Codex.